Category: Software Architecture

Development, Object Oriented Programming, SDLC, Software Architecture

Unit testing: climbing the Uphill road

This article is not about discussing the basics of unit testing or simplifying the concepts, nor it is about merits of the practice. Unit testing methods have evolved quite a bit, with many books and online content. However, the real world practice of Unit testing can be an uphill task in several contexts, due to different reasons, even after how the ecosystem around Unit testing has matured quite a bit.

Unit testing is both an Architectural as well as DevOps concern. Tactically both these departments strive to get the software development operations to effectively incorporate Unit testing.

What are some of the challenges ?

  1. Brownfield vs. Greenfield : Unit testing is easier to adopt when you are starting a new application. The reason being an application needs to be written in a certain way, applying principles like S.O.L.I.D to be able to Unit test it effectively. There are a few key programming knowledge areas which need to be understood well before starting Unit testing correctly, like Interface driven programming and Dependency Injection. The industry is full of so called ‘Brownfield’ applications or simply existing production applications which may not have been written using some of the best practices. These Brownfield applications can become major barriers of entry into Unit testing. Software Engineers who are involved day to day supporting these applications often find it difficult to introduce Unit testing into them because they need to be refactored before doing so.
  2. Time : Unit testing applications can be time consuming, requiring additional development time to be factored in. Often this upfront time is seen as additional cost to development without realizing that, there could be long term benefits like reduced QA footprint and automated regression tests. Hence a technical leadership which creates a culture of Unit testing by coaching the stakeholders on benefits of Unit testing has to be fostered by organizations.
  3. Training: To Unit test effectively, software engineers need to have knowledge of Unit testing basics like creating Mocks, Code Coverage and the AAA pattern ( also known as Arrange, Act and Assert ) . The lack of this knowledge itself can be a barrier even if the first two barriers do not exist. Hence training on Unit testing fundamentals and the available Unit testing frameworks needs to happen.
The Uphill task of Unit testing

The industry is full of so called ‘Brownfield’ applications or simply existing production applications which may not have been written using some of the best practices. These Brownfield applications can become a major barriers of entry into Unit testing. Software Engineers who are involved day to day supporting these applications often find it difficult to introduce Unit testing into them because they need to be refactored before doing so.

All the above challenges need to be overcome to create an atmosphere and mechanism of regular Unit testing.

How do we overcome the challenges ?

  1. A brownfield application which does not lend itself to Unit testing through it’s design will have be refactored first – piecemeal by piecemeal to facilitate the testing. Refactoring can include anywhere from making the code more object oriented, removing deep coupling, adding dependency injection and creating interfaces. Brand new code within the project can be written keeping Unit testing in mind. The more monolithic and deep coupled the code, more refactoring has to be done. It is best to chew at it slowly – over a period of time code will improve. Scrapping a brownfield completely to start a new greenfield application is not always an easy decision. Hence refactoring existing code for improvement one step at a time, can be more cost effective and beneficial.
  2. ‘Time’ is the one of the most negotiated element during software development. Most stakeholders like Product Owner and end clients will want the application deployed ‘yesterday’. In such a situation anything that adds more time to development can mean negotiation, conflict and stress. It is very normal for software engineers to give up on Unit testing when time is a constraint. A strong technical leadership committed to building consensus over Unit testing is critical to overcoming the time constraint- time spent upfront will save time later. The most significant benefits are as stated earlier Reduced QA time, Automatic regression and Better product quality.
  3. Unit testing does not come naturally as part of software development. It is still a habit which has to be developed and cultivated- training is also required to understand techniques of Unit testing. Lack of knowledge itself can inhibit Unit testing to happen even if the above two situations don’t exist. Often the difference between Unit testing and Integration testing are not understood. A culture of training and learning Unit testing has to be created. Team members who are ahead in Unit testing can be appointed as ‘coaches’ in Unit testing. Unit testing demos, presentations and discussions must be organized regularly to create the energy and enthusiasm around it. Technical leaders must ‘call out’ above and beyond Unit testing efforts; Incentivize or reward Unit testing efforts. An overarching policy of ‘incremental’ code coverage can be set, gradually increasing percentage code coverage. As needed ‘time’ must be allocated for the purpose of unit testing within the development cycles with the help of project managers.

A 100% code coverage may or may not be necessary based on the type of code or type of project. It’s a great goal to have, however it’s more important to test code for where rules, algorithms, calculations and complex logic need to be tested thoroughly. If time is a constraint decide where there is more value in Unit testing, and Unit test that part of the application.

An overarching policy of ‘incremental’ code coverage can be set, gradually increasing percentage code coverage. This way as the team matures into Unit testing, code coverage requirements are increased. Team members who are ahead in Unit testing can be appointed as ‘coaches’ in Unit testing. Unit testing demos, presentations and discussions must be organized regularly to create the energy and enthusiasm around it. Technical leaders must ‘call out’ above and beyond Unit testing efforts; Incentivize or reward Unit testing efforts.

A culture change like Unit testing can only happen when there are strong technical leads committed to the quality of the software, willing to go above and beyond to achieve that excellence. They have to be leaders willing to see beyond self-interest and work towards consistently evangelizing the practice.

Software Architecture, Technology Leadership

‘Core Architecture’ function : why, what and how

Core Architecture function is not a new concept in many software companies. Systems which support a business are engineering products which ideally are built on top of many building blocks. The more the complexity of systems, more you need common building blocks which act as ‘Services’ or ‘Micro Services’, allowing new applications to be built quickly with them. While many companies have come to learn the value of establishing a core architecture function, several organizations have not yet realized the benefit of investing in such a structure. The reasons can be different depending on the company history and culture.

Why do we need a Core architecture group?

This model facilitates cost effective application development by promoting re-usability, and reducing redundancy. Often groups within a company are seen solving the same problems over and again in different ways. While autonomy and reinvention is necessary for creativity and improvement, it can be expensive in many cases when instead of  an existing solution being reused, it’s built all over again. In this age of Agility in producing digital products, reinventing the wheel often means lag in time-to-market with high upfront cost in development. Organizations when are totally reliant on automation and digitization, having building blocks or services which provide a ‘platform’ for quick application development is essential for nimbleness and speed to market.

In this age of Agility in producing digital products, reinventing the wheel often means lag in time-to-market with high upfront cost in development. Organizations when are totally reliant on automation and digitization, having building blocks or services which provide a ‘platform’ for quick application development is essential for nimbleness and speed to market.

It is also important that today’s digital products address the concerns of scale upfront. Products have to be built to scale, and a core dedicated architecture function is better positioned to streamline the architecture of applications in that direction. Development leads can use the guidance and assistance of dedicated architecture functions in addressing these concerns.

Software engineering and architecture standards, guidelines have to be established, shared, ensured and enforced as needed. Technology leaders who are empowered to make executive decisions must develop and communicate certain high level coding and architecture standards and practices, which keep the underlying code consistent, standard and of high quality.

What are the responsibilities of a core architecture group ?

A Core architecture group is a highly functional group which interacts and collaborates with all the stakeholders. The responsibilities will entail both strategic and tactical.

  1. Understand thoroughly the business capabilities of the organization, how information flows.
  2. Map and list all the core services that cut across all business capabilities of the company.
  3. Communicate on an ongoing basis the required services and their value.
  4. Discover already existing core / common services by collaborating with different teams. There could be multiple flavors of the same service, however bringing them all to the front will likely cause some of them to be reused. Those which are the most used can be narrowed down as final core services. Hence create a common repository of all these services, catalog and document them. Share the knowledge and documentation, provide links via source control, shared libraries or API endpoints.
  5. Plan and build new core services and publish.
  6. Evangelize core services, be the facilitator of systems integration of these services. This is a challenge in itself. It might be easier to build services, however harder to get them integrated into existing systems- an easier strategy then is to integrate services in new applications.

corearchitecture

In addition as the team grows and matures, it can take on other architecture functions like:

  1. Ensure application and systems architecture will be able to scale via reviews, testing and metrics. Consistently work with development leads in that direction.
  2. Establish and ensure coding and architecture standards.

The function can extend to encompass more tenets of architecture like performance, resilience, reliability and more.

How do you go about building a core architecture group ?

Execution is key- if a core architecture function is integrated well with the day to day development operations, a solid foundation is built for systems for the future.

  1. If budget allows it, form a team of software architects and engineers dedicated to this function. This can be a very small group to begin with, even starting with one expert architect can be good. And then this can be grown to a bigger group as needed.
  2.  If not, appoint technical leads , lead developers or technical managers as part time architects who take on the job of core architecture. There might be challenges with time management with day to day work, however this is a collective effort. Individual responsibilities can be assigned. These responsibilities and tasks are not outside of mainstream development work, they get integrated into the development pipeline and followed up on. This way there is full accountability. In fact a structure like this can be an advantage because systems integration is easier, the managers and leaders are already involved in developing the core services themselves.

Technology leadership of a company has to be vested in the idea of a Core architecture group. This is critical to the success of Systems that support the business functions. Product definition, product development and systems architecture all need to work together towards building products which scale and stand the test of time.

Software Architecture, Technology Leadership

Building a strong technology team
Every company today is a technology or software company. Software automation is the backbone of business operations today. The lines between business operations and software development are blurring because the two groups work together more closely than ever. Technology leaders have a tremendous responsibility of developing a futuristic digital vision, and accordingly building a strong technology team which can accomplish the vision.
vision-exercise-1
The goal of building a 5 year technology vision which translates into a solid technology road map can be lost even in companies who believe they are ‘tech’ companies. The daily pressures of production support, development operations and releases can bog down most of the technology managers. However a strong technology leader makes it her most important responsibility to build a technology vision and road map which takes the company to the next level of success step by step, avoiding major technical debts. The leader must develop a vision along with her other technology leaders who are her reports or peers so they can be the torch bearers of the vision. The vision has to trickle down and across.
The product vision and technology vision will together guide in building a team which will execute both, to a successful outcome.
A technology road map addresses technical debts, refactoring, migrations and upgrades, new technology evaluations, tool assessment and introductions, and any other relevant technology initiatives which are essential to technology growth for the company. The product vision and technology vision will together guide in building a team which will execute both, to a successful outcome.
So, what does a strong technology team composition look like ?
People talent is core to a company’s growth-  developing a team which aligns with the best technology practices and future vision is key to building a strong team. A technology leader, manager can strengthen her team by assessing what the current team composition and talent spread is. This assessment exercise should be periodically repeated until an optimal skill and experience mix is reached.
                                                      team    

A technology leader can strengthen her team by assessing what the current team composition and talent spread is. This assessment exercise should be periodically repeated until an optimal skill and experience mix is reached.

 

  1. Make a list of skill sets you want to have in your team.
  2. Determine which skill sets exist and which do not.
  3. Where are the strengths ? Where are the weaknesses- you want to induce talent in the team which will complement the existing skill set. Hire people from outside who have these new talents, when they come, they naturally rub off on the existing team. This is a huge motivator – peers who bring new ideas and skills from which one can be inspired and challenged. A natural growth occurs.
  4. Determine what experience levels exist. Too many Juniors can lack the experience and domain expertise to deliver well to your business context. Too many seniors can create Silos- they are opinionated and  often comfortable in their set old ways. Hence a careful examination of team composition is always necessary in determining team morale and growth.
  5. Attract and hire fresh talent- fresh graduates and juniors are highly motivated, open and enthusiastic. You need a good mix of Juniors, Mid-Level and Senior staff. You have to have few Senior experienced leaders and mentors, some Juniors and rest Mid-level. A 30 % experienced, 40% mid, and 30% Junior approximately can be a healthy composition which will keep the team motivated , mentored and productive. An imbalance or dominance of any category can lead to side effects which are not healthy.
  6. Form a ‘Core architecture team or function’. Break ‘Silos’ by creating a formalized core architecture team, function or platform which establishes re-usability, reduces redundancy, and builds common services.

Form a ‘Core architecture team or function’. Break ‘Silos’ by creating a formalized core architecture team, function or platform which establishes re-usability, reduces redundancy, and builds common services.

What about professional growth, nurturing home grown talent ? 

A leader has to create an impact on the team in many different ways for professional development.

  1. Lead by example : you can demonstrate that as a leader you walk the talk. Demos, presentations, proof of concepts provide actual examples of what is being proposed and evangelized. People follow examples better than persuasion.
  2. Be hands on, deep and wide technically. A technology leader when ‘speaks’ to technology very well, often can make much greater impact.
  3. Appoint coaches on topics to promote learning. For example , say you want to spread Unit testing practices. Pick people in the team who are ahead in that, as appointed coaches. Likewise for example  ‘Agile’, ‘Build automation’ or any best practices where learning needs to be facilitated.  This can also foster a culture of learning from peers.
  4. Call out, above and beyond efforts.  Provide a platform for star performers and outliers to ‘show and tell’. Interesting events like Lunch n learns, ‘Coffee chats’ or other group meetings can be organized where team exchanges ideas in a more casual setting.
  5. Consensus building: let’s face it, in technology multiple view points exist. People can get passionate about their opinions- a leader may need to be patient and persuasive which of course is not easy. Often there is one solution which suits the context most, towards which the consensus has to be built. White boarding the context and various solutions, and mapping the most suitable in that situation will help build consensus.

One article can not cover the vast topic of how strong technology teams can be built, however everything starts with a vision and a road map. The leader then aligns the team with this vision consistently.  An assessment and measure of team skill and experience spread, will help carve a plan for building a strong technology team. Stay tuned for more on this topic – happy team building !

Design Patterns, Development, Software Architecture, Technology Leadership

Collaborating teams build systems that collaborate

Information systems of a company are a reflection of the communication patterns within the organization. The more teams communicate with one other cohesively, these systems will connect and grow together more as a result. In today’s world of digital transformation and data intelligence, it is imperative that multi function organizations communicate and collaborate, so systems built by the development staff will bring the necessary business intelligence and scale. This cohesive intelligence is critical to further growth. It is very common in multi function organizations for ‘Silos’ to develop over a period of time. These ‘Silos’ focus successfully on one aspect of the business, however they fail to connect with other systems in the workflow such that it reflects the customer journey. This ‘disconnect’ can create many black-boxes producing their own data, which as a whole brings minimal value in the long run.

It is very interesting that many popular methodologies and architectural patterns have evolved which fundamentally solve this problem of communication. Let’s take DevOps for example. DevOps is designed to have better collaboration between Development teams and Network operations. Although they are independent in function, lack of communication between them results in surprises, errors and continuous finger pointing. This can be very expensive operationally leading to client dissatisfaction. Today DevOps has had great success which leads to test, build and deployment automation. This in turn increases speed-to-market and system reliability.

In today’s world of digital transformation and data intelligence, it is imperative that multi function organizations communicate and collaborate, so systems built by the development staff will bring the necessary business intelligence and scale as well.

Agile development methodologies solve the collaboration problems between all disciplines of an organization. The SCRUM methodology with it’s different ‘ceremonies’ brings all relevant departments together in one room regularly. From Sprint Planning to Sprint Retrospective, different departments like products, development, QA, and user experience come together to discuss topics from requirements to ‘lessons learnt’. This collective, methodical way of communication leads to better product definition, risk mitigation, estimation and release planning. Everyone is in a continuous improvement and feedback loop, improving deliveries significantly.

collaboration

Let’s take Micro-services architecture, for example. This style of architecture was embraced by many companies in an effort to have small teams become autonomous by fostering a loosely coupled architecture connected via independent services. Again, at a high level team structures and their communication patterns dictate how the Enterprise architecture shapes. Netflix adopted the Micro-services architecture to increase speed-to-market which led to a social culture of small autonomous teams collaborating together.

Companies don’t just build products and offer services , they build professional communities and offer personal growth.

Any organization which looks to build information systems that work together, while they are independent units, has to build a communication culture and team structure which can facilitate such systems. Cohesive systems bring business intelligence while loose coupling allows them to scale. Cohesion comes from continuous collaboration and loose coupling comes from small autonomous teams. Adopt methodologies and architectural patterns which bring teams and people together. Companies don’t just build products and offer services , they build professional communities and offer personal growth.

Design Patterns, Development, Object Oriented Programming, SDLC, Software Architecture

Program to an interface , not an implementation

I have been lately discussing SOLID in my previous posts – some of the basic principles of OOD . Recently while doing my project work , we had to decide between Entity Framework  or NHibernate which are popular ORM layers in .Net framework .  The decision was not easy , we got stuck at Second Level caching support …and could not reach any decision right away. I started thinking that may be for now we have to write our layer in such a way that we choose one ORM , and then we can switch to a different one worst case if need be. Ideally a situation like this should not arise , but if it does happen , you need to be able to do it.  Once again I felt how a very fundamental OOD principle could come in handy –

Program to an interface , not an implementation.

These words above can be very ambiguous and abstract when you just read them .

However when seen from a context , you understand how powerful this is , and how it can increase flexibility and ability to switch . Seen from my own situation where we needed the flexibility to switch data access mechanism if need be, let’s understand this by constructing a scenario. For example , a common problem could be implementing a subscription mechanism for a data service that your system may provide. Users can subscribe to the data service and get notified when a change occurs. We need to persist the subscription information to the database , where you will need to use some database access mechanism.

As usual there is a presentation layer that gathers some subscription information and passes it along to the data service which persists the information to the database . For simplicity’s sake , let’s say we have a SubscriptionService , which is our data service for persisting subscriptions . We can discuss this further in the context of an ASP.Net MVC application – where a View is our Presentation layer through which Subscription details are collected. A controller action method is typically invoked to pass along the information to the server.

We can assume for our article purposes that our application provides notifications on Food Recalls. So the member user to our website subscribes to recalls for a certain type of food issued by different organizations like FDA etc. The Subscription in simplicity could be :

Please note : all code is pseudo only , this is not a working solution that can be downloaded and built.

public class RecallsSubscriptionService
{
    Boolean Subscribe( int userId, string food_type, string organization)
    {
           // data access code to insert subscriptions
           return false; 
    }         
}

Most of the times the controller action method would look something like this:

public class SubscriptionController : Controller
{
        [HttpPost]
        public ActionResult Subscribe(int userId, string food_type, string organization)
        {
            try
            {
                 SubscriptionService myservice = new SubscriptionService();
                 myservice.Subscribe(userId, food_type, organization);

                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }
}

So , we make a decision we will use Entity Framework 6 to implement our data access to store subscription information. The above code will work fine . The code goes into production . However later we decide that due to certain project requirements we have to switch to NHibernate. This is a tough situation – our controller here , who is a client of the SubscriptionService , is heavily dependent on instantiating this specific service which accesses the database with Entity Framework 6. Although we expected the problem could arise we didn’t design our system for this flexibility. Even though we encapsulated the data access code into a Service , we did not free the client from the implementation of data access because the client program is indirectly tied to EF implementation.

We need to make some changes , so our controller is independent of the future changes that could happen to the database access mechanism. To bring transparency into how data access may happen from a client’s perspective we need to introduce interfaces. We write an interface instead for the SubscriptionService :

interface IRecallsSubscriptionService
{
   Boolean Subcribe(int userId, string food_type, string organization);       
}

We could write two implementations of the above interface or we could just use the same implementation we had earlier , and replace it with NHibernate.

public class RecallsSubscriptionServiceEF
{
       Boolean Subscribe(int userId, string food_type, string organization) 
       { 
                //   implement using EF ;
                return false;
       }         
}

public class RecallsSubscriptionServiceNH
{
       Boolean Subscribe(int userId, string food_type, string organization) 
       {
              //implement using NH ;
              return false;
       }         
}
/*( not that the above approach is recommended , where you keep 
two implementations available for the same requirement. 
This is for understanding purposes only )*/

The above mechanism allows us to drive the Subscribe method call through the IRecallsSubscriptionService interface. In order to effectively use the method above , we will need to pass IRecallsSubscriptionService as a parameter to the controller constructor and use dependency injection in this scenario to have the right concrete class to be instantiated during run-time. I will not dive deeper into that because it is outside of the scope of this topic.

This is the whole basis of Dependency Inversion and Injection ( this is also the ‘D’ in SOLID ): here we program to an interface , not an implementation as we saw above. This gave us the flexibility to change our implementation completely without changing the client code. So the basic idea is programming to an interface decouples the client from the internal implementation freeing calling programs from knowing the internals leading to flexibility in changing implementation as the need arises.

Even in scenarios where there are published APIs , when you use objects  go up in hierarchy to program to the interface as opposed to the concrete class. So if you are using a List object and comparing individual strings-  then if this object implements IComparer , then program to IComparer –

instead of writing:

List myList = new List();
myList.Compare( myList[0] , myList[1]);

//Write as :

IComparer myList = new List();
myList.Compare( myList[0], myList[1] );

//This gives you the freedom to use a different flavor of Compare method if you need to ,

IComparer myList = new Array();
myList.Compare( myList[0], myList[1] );

The advantage of the above is ability to switch different comparison methods if they are available. And also test program can easily switch different implementations and see what works the best.

We also need to understand that “Program to an interface” should not be taken literally . Even Abstract classes can act as interfaces in this context and give us the same flexibility.

Interfaces should be used wisely and only when needed. If there is no potential for an implementation to ever change there is no need to bother with interfaces. For example , a Utility class that converts a string to a number. There is no need to write interface to this . Interfaces should also be used in projects where testability is a big concern and mocking may be required.

Design Patterns, Development, Object Oriented Programming, OO, SDLC, Software Architecture

SOLID conclusions with ISP and DIP

In my last post we went over LSP ( Liskov Substitution principle ) , how it helps achieve Subtype Polymorphism. We learnt how to think in terms of client programs and how client’s call to  programs can influence the quality and design of applications. The SRP and OCP are foundational principles on which LSP and the next one we discuss today , ISP manifest themselves.  It is not enough if Single Responsibility and Open Closed are understood – the rest of the three principles are where you see their applications and extensions. LSP , ISP and DIP all three teach us how to design from a client’s point of view. Uncle Bob calls it as “Clients exerting forces “  . 

The interface-segregation principle (ISP) states that no client should be forced to depend on methods it does not use

ISP helps formulate mechanisms on how interfaces should be segregated so the same interface can be useful to different clients. It’s a very powerful thought that can bring strong results. Single Responsibility talks about writing interfaces that have very cohesive functions . ISP takes it one step further and gives concrete ideas that give rise to reusable interfaces . This is where the relationship and the difference between SRP and ISP exists .

So how does ‘Segregating’ Interfaces help the clients ? Interfaces are meant to represent a certain type of behavior to the client and by virtue of their contractual representation promote pluggability. So when interfaces represent more than one type of behavior , they provide more than what a client needs . This leads to the interface becoming incapable of being used for plug-in purposes. Also they become ‘Fat’ in nature , with unncessary behavious not useful in the client’s context. Basically this is solidifying more on the SRP and OCP and stressing a whole lot more on how interface contracts should represent one type of behavior. Almost all patterns have a basis in SRP , OCP and ISP. Let’s say we are writing a class to represent a Persistence Medium. One of the most popular persistence medium is Database . So is XML . And a lot of applications use simple JSON files to store simple content.  Say , we start out by writing a PersistenceMedium class. So a simpe IPersistenceMedium looks like this :

Code is pseudo only , to describe the principle , not a working , compiled example :

// IResult is an imaginary interface 

interface IPersistenceMedium
{
       string fileName { get; set; }
       string connectionString { get; set; }

       void Open();       
       void IResult ExecuteQuery(string query);
       void IResult ReadFile();
       void Close();
}

//So our database class can be written like this:

public class Database : IPersistenceMedium
{
    private string _connectionString;

    public string connectionString
    {   get{ return _connectionString; }  
        set{ _connectionString = value; }    
    }

    public void Open(){  /* database open connection code */ }
    public IResult ExecuteQuery( string query );
    public void Close(){  /* database close connection code */ }
}

// The JSONStore can be written like this :

public class JSONStore : IPersistenceMedium
{
     private string _fileName;

     public string fileName
     {   get{ return _fileName; }  
         set{ _fileName = value; }    
     }

      public void Open(){  /* open a JSON file code */}
      public IResult ReadFile();
      public void Close(){  /* close file code  */}
}

See what happened above ? The Database class could not use ReadFile() and fileName and JSONStore could not use ExecuteQuery() and connectionString . Although both are variants of a PersistenceMedium behaviour , they are unnecessarily clubbed together from the perspective of Database and JSONStore classes which are the clients of IPersistenceMedium.

A Better way would be :

interface IFileConnection 
{ 
     string fileName { get; set; }
     void Open();
     void Close();
}

interface IDatabaseConnection 
{   
      string connectionString {  get ; set; }   
      void Open();
      void Close();
}

interface IDBOperation
{
     IResult ExcecuteQuery();
}

interface IFileOperation
{
      IResult ReadFile();
}

Now this provides interfaces that can be specifically used for Database or JSONStore because we segregated them keeping in mind different clients / client groups. The interfaces which can be used for JSONStore can be used for XML or any other type of file store. Similarly the interfaces that got written for Database can be used for any type of database , SQL , Oracle or NoSQL . The interface is less fat , with interfaces ‘Segregated’ strictly based on different client usages . This is SRP in effect, by using ISP.  What are the different ways of using these with the Clients ? One obvious way is multiple inheritance.

public class JSONStore : IFileConnection , IFileOperation
{
    private string _fileName;
    public string fileName
    {   get{ return _fileName; }  
        set{ _fileName = value; }    
    }

    public void Open(){ /* open file*/ }
    public IResult ReadFile(){ /* Read File */}
    public void Close() { /* Close File */ }

}

public class Database : IDatabaseConnection , IDatabaseOperation
{
    private string _connectionString;
    public string connectionString
    {   get{ return _connectionString; }  
        set{ _connectionString = value; }    
    }

    public void  Open() { /* Open Connection */}
    public IResult ExecuteQuery(){  /* execute query to obtain results */}
    public void Close(){ /* Close Connection */}

}

The above JSONStore could be very well be written as FileStore , in that case different FileStores can be used and IResult representing different result types form different types of files.

There are different ways to implement the above without multiple inheritance. One way is to use something like a Strategy pattern where IFileOperation has concrete classes for JsonFileOperation and XmlFileOperation – because each may have subtle read differences. XML requires special parsing and JSON is more of a string representation.

We have been able to establish in many different ways the value of SOLID – how it  leads to good design practices and understanding of patterns.

I will conclude without diving into Dependency Inversion – there are fantastic blogs including Uncle Bob’s report. Dependency Inversion distinguishes itself by establishing how layers should interact  without depending on each other. Again a powerful concept that has led to great programming practices including Test Driven Development and several patterns that facilitate the principle. SOLID is definitely worth your time !

Design Patterns, Object Oriented Programming, OO, Software Architecture

Way to Patterns : even more SOLID

In the last post we saw how OCP facilitates extensibility and reusability . OCP is the foundation on which several patterns have been written. The Strategy pattern is a great example of OCP where subclasses are written based on different algorithms. The manifestation of OCP happens in the third SOLID principle , the ‘L’ as we know ,  Liskov Substituion principle – perhaps the more involved and less understood principles in SOLID .

We saw how SRP can lead to OCP – LSP takes OCP and establishes clear rules that will ensure polymorphism is accomplished correctly. LSP attempts to achieve what we call subtype polymorphism through it’s rules. In short we can represent this in pseudocode – a client call to a subtype method call , through a base class interface:

public class Supertype{   public virtual outparam SomeMethod( inparam );   }     
public class Subtype : Supertype { public override outparam SomeMethod( inparam );  } 

 //Client call:   
 Supertype baseType = new Subtype();    
 outparam = baseType.SomeMethod(inparam);

Liskov Substitution statement  translates to : Subtype(derived type) must be behaviorally equal to their base types. They must be usable through the base type interface without the need for the user to know the difference.

LSP needs to be understood from a client’s perspective . Client here means : Calling programs , Users of your interfaces and abstract classes within the organization  or outside the organization. A Client perceives the behavior of a class through methods of a class : arguments passed , value returned and any state changes after the method execution. So basically to be able to use a subclass / subtype in place of a superclass/supertype the sub type successfully needs to preserve argument requirements and return expectations by the client.  A client code that gets written keeping in mind the Supertype to call it’s method should not change or break when replaced with subclass method calls . Compilers do enforce Signature compliance when methods are overridden from abstract classes . However internally within the implementation if arguments or return values were treated in a manner that could break the client code , the code is in violation of LSP because essentially the contract with the client was broken . Compilers typically will not catch these violations.

It is the programmers responsibility to ensure LSP compliance for the most part.  In order for the internal subtype behavior to keep in consistency with supertype behavior , these principles were formed.

There is a very subtle and interesting nuance that one needs to understand here. You could very well write a ‘Superclass’ , and then write a ‘Subclass’ – override the Superclass method to give a specific implementation. Use the subclass in your programs to execute the subclass specific method. You may never see anything wrong up until you expect the subclass to be a ‘subtype’ of the Superclass which is a Supertype. It’s when a ‘subclass’ is expected to become a ‘subtype’ is when LSP comes into play.

A lot of blogs have been written to explain these rules.  I have cited at the end some good ones in order to understand them with code examples : instead in this blog let’s try and understand some of the confusing rules that mostly I have seen people asking questions about .  Let’s just list all of them first :

  • Contravariance of method arguments in the subtype.
  • Covariance of return types in the subtype.
  • No new exceptions should be thrown, unless the exceptions are subtypes of exceptions thrown by the parent.
  • Preconditions cannot be strengthened in the subtype
  • Postconditions cannot be weakened in the subtype
  • Invariants must be preserved in the subtype.
  • History Constraint – the subtype must not be mutable in a way the supertype wasn’t.

Now, let’s take just the two which seem to confuse most people :

  • Preconditions cannot be strengthened in the subtype.
  • Postconditions cannot be weakened in the subtype.

Preconditions apply to arguments which will be used as part of the implmentation. Postconditions mostly relate to return values or the state after the implementation is executed. Preconditions are requirements on users of the functions, while postconditions are requirements on the functions themselves. Preconditions get executed before the actual implementation is executed , whereas postconditions are executed after.

Preconditions cannot be strengthened in the subtype.

Wikipedia explains this as :

In the presence of inheritance, the routines inherited by descendant classes (subclasses) do so with their preconditions in force. This means that any implementations or redefinitions of inherited routines also have to be written to comply with their inherited contract. Preconditions can be modified in redefined routines, but they may only be weakened. That is, the redefined routine may lessen the obligation of the client, but not increase it.

What is the obligation of the client ?  The arguments that need to be passed  , is the obligation of the client. If the preconditions  are set in such a way in the subclass method  that the choice of the arguments which can be passed from the client is lesser or restricted then you actually strengthened the precondition .  This increases the obligation of the client.

Let’s understand this with an example. We will modify the IFormatter interface from the last post to an abstract base class with some implementation.

 abstract class Formatter{            

         public virtual string Format( String message)
         {
                if ( String.IsNullOrEmpty( message ) ) 
                    throw new  Exception ();
                // do formatting
         }      

     }
    // strengthened precondition
    public class MobileFormatter : Formatter{

         public override string Format( String message)
         {
                if ( String.IsNullOrEmpty( message ) || message.Length > 250  ) 
                    throw new  Exception ();
                // do formatting
         }

    }
    // weakened precondition
    public class MobileFormatter : Formatter
    {
        public override string Format(String message)
         {
                if ( message == null  ) 
                   throw new  Exception ();
                // do formatting
         }

    }

As we see above the MobileFormatter placed more restriction on the arguments in the strengthened precondition – this will force the client to change their code to accommodate for this if they want to avoid getting an exception.  So behaviorally the base and subtype are different.

In the weakened precondition what happened is that the client now does not need to accommodate the code for MobileFormatter, the argument that gets passed to MobileFormatter , works for base Formatter as well because the validation in Formatter is stronger or the validation in MobileFormatter is weaker.

Postconditions cannot be weakened in the subtype.

Wikipedia explains this as :

In the presence of inheritance, the routines inherited by descendant classes (subclasses) do so with their contracts, that is their preconditions and postconditions, in force. This means that any implementations or redefinitions of inherited routines also have to be written to comply with their inherited contract. Postconditions can be modified in redefined routines, but they may only be strengthened. That is, the redefined routine may increase the benefits it provides to the client, but may not decrease those benefits.

Let’s understand this with a code example:

   abstract class Formatter
    {

        public virtual string Format(String message)
        {

            // do formatting
            return message.Trim();
        }

    }
    // weakened postcondition
    public class MobileFormatter : Formatter{

         public override string Format( String message)
         {

                //do formatting
             return message;
         }

    }
    // strengthened postcondition
    public class MobileFormatter : Formatter
    {
        public override string Format(String message)
        {

            //do formatting
            return message.Trim().PadLeft(5);
        }
    }

What we see above in the MobileFormatter is that the postcondition got weakened by removing the Trim method. This provides the client less than what was provided in terms of the result .

Then to correct it , we strengthened the postcondition by adding left padding. This does not require the client to change any code , however the code gets the extra benefit of padding. The above example is rather crude but serves the purpose of explaining .

There is a very interesting pattern called Template pattern accomplishes LSP via template methods written inside a base class which are overridden in derived classes.  For now , this is enough to contemplate about – more in the next blog .

Here are some really good blogs on Liskov that discuss other rules as well:

http://www.ckode.dk/programming/solid-principles-part-3-liskovs-substitution-principle/#contravariance

http://msdn.microsoft.com/en-us/magazine/hh288081.aspx

Until then happy programming !

Design Patterns, Development, Object Oriented Programming, OO, SDLC, Software Architecture

Finding the way to Design Patterns : more SOLID

So continuing into the process of finding our way into design patterns from my last post , we will try and unfold SOLID a bit more. Some of the SOLID principle interpretations and applications can be very subjective and a matter of debate. How do you know the classes that you wrote have adhered to the Single Responsibility Principle ? Is there a way to determine ? What does Single Responsibility exactly mean?  How far do you try and take these things…blah ..blah.

There needs to be a balance in everything of course.One needs to find a mid way between over-engineering and under-engineering. We need to create small classes with very few cohesive/related functions without getting carried away by having so many classes that we cannot manage those either. At the same time , understanding exactly how to create classes with just one relevant behavior or few cohesive functions can get tricky. It’s important to ask the question while writing a class , what is it that will potentially change in this class later , that can be re-factored into a separate class , so minimal changes / or no changes need to be made to the existing implementation when the change needs to be made.

It’s important to ask the question while writing a class , what is it that will potentially change in this class later , that can be re-factored into a separate class , so minimal changes / or no changes need to be made to the existing implementation when the change needs to be made.

If we take the Logging example that we discussed in the previous post , we discussed three functions a logger can do. Initializing a medium to log , Formatting to the medium itself  and Writing to the medium . So, they all look like related functions don’t they ? So they all can go in one class , which is a violation of SRP . If we take one step further into re-factoring  perhaps it’s easy to recognize right away that there are different mediums to log , each requires a different method to write to itself. So we create separate classes for the medium . Yes , we applied SRP here.

What about formatting ?  Can formatting change ? Yes, it can . Say we need to add a new logging medium called Mobile Device. To the mobile device , you want to send text messages whenever severe conditions occur. Doesn’t the format of what goes into a database differ from a mobile device ?  Also , later down the line the potential users of our Logger may require that they want the format of the message a little different. Now if we did not separate the format function into it’s own class , we have it as part of the class that writes to the medium or worse as part of the Logger class. Logger class is actually our client facing class that the client would use to log messages . Just to change  formatting , we have to go and change this Logger class or the medium classes.

At this point we need to consider  whether it’s worth writing something like this:





   1:  interface IFormatter {
   2:   
   3:  public string Format( string message );
   4:   
   5:  }
   6:




and the logger could do something like this :






   1:  public class Logger{
   2:   
   3:  public Write( IFormatter formatter){}
   4:   
   5:  }
   6:




Or let’s go couple of steps further along these lines,






   1:  public interface ILogMedium{
   2:   
   3:  void Write(String Message);
   4:   
   5:  }
   6:








   1:  public class LogToDatabase : ILogMedium{
   2:   
   3:  public void Write(string message){
   4:   
   5:  // medium specific logging
   6:   
   7:  }
   8:   
   9:  }
  10:








   1:  public class Logger{
   2:   
   3:  ILogMedium _logTodb;
   4:   
   5:  IFormatter _formatter;
   6:   
   7:  public void Logger( ILogMedium logToMedium,  IFormatter formatter )
   8:   
   9:  {
  10:   
  11:  _logTodb = DBMediumProvider.Create(); // DBMediumProvider could be a creation class
  12:   
  13:  _formatter = DBFormatProvider.Create(); // DBFormatProvider could be a creation class
  14:   
  15:  }
  16:   
  17:  public Write(String message){
  18:   
  19:  _logTodb.Write( _formatter.Format(message) );
  20:   
  21:  }
  22:   
  23:  }
  24:




Please note : The code above is not a working solution. It is only like pseudo code to demonstrate the thought process .


The advantage of the above is we kept the formatter completely separate from the medium , as well as the Logger class. This allows us to plug in new mediums , formatters and configure them based on our needs. Also , if there are bugs it’s easier to fix a specific class as opposed to one big class which could potentially break other functions.


This brings us to the Open Closed principle , which is the next one and the ‘O’ in SOLID as we all know.


A consistent use of SRP can lead to OCP , which simply states: A class should be open for extension but closed for changes. This does not mean that classes should be completely sealed for change , it means that the class should be in a state where only bug fixes should be made and new functions should be added via new classes , minimizing implementation changes to the existing classes.


Words should not be taken literally here : once you wrote the class does not mean that it cannot be changed at all : however we should get to a point that , when behavior changes in predictable ways, you should not have to make several changes into a single class or several classes in the system. An ideal situation would be where you achieve the change by adding new class / code rather than changing existing code . For anyone who has been in programming for a few years supporting production systems , this will make a lot of logical sense.


Whatever we discussed above with Logger example with reference to SRP will apply to OCP as well , because OCP can be achieved by applying SRP consistently. So had we written the formatting in the Logger or the individual medium classes we would not be able to add new formatters or change existing formatting without changing the Logger or the mediums classes , plus mix and match formatting with mediums . The way we achieved OCP with Logger example is we gave the Logger a Single Responsibility of writing to the medium. We gave the Medium classes a Single Responsibility of initializing / creating the medium and specifically write to that medium as well. And then OCP came into effect when we made it possible for new formatters to be added to the system by simply implementing the interface IFormatter and adding that class to the system as a plugin. So , when a user wants to use the new Formatter , she can do it through the configuration system and that formatter will get automatically used which needs to be implemented through some creation classes of course , which is a separate topic – an example is Factory Method pattern.


Several design patterns use the SRP and OCP , and following the above two will put you in the mode of clean and efficient code . Some popular patterns like Strategy , Factory are all based on OCP . We will continue with this discussion in the next post , happy programming !


Few references :


Wikipedia definition Open-Closed


Interesting read on OCP by Jon Skeet


	


	



			
				


	

	

	

		

						

														
						Design Patterns, Development, Object Oriented Programming, OO, SDLC, Software Architecture					
									
							

			
			
Finding the way to Design Patterns : SOLID

		

	



	

	
In my previous post on design patterns I discussed about why it’s a challenge for developers / organizations to adopt patterns as part of their development practices. I also had suggested that a dedicated effort to re-factor code should be made continuously as part of software life cycle especially in the early to mid-stages of development. Having said that, how do you go about re-factoring? How do some of the object oriented principles and design patterns help with re-factoring? So, if re factoring is important, the object oriented mechanisms that allow and facilitate this are important as well. In conclusion the learning needs to happen, slowly and steadily – as a result it will start becoming a habit to incorporate some of these patterns related principles.


I guess the challenge is where do you begin? There is a ton of information on the web, it’s all too overwhelming, scattered and fragmented. You need a have a structure and if you just pick up the Gang of Four book (our bible for design patterns), it can seem rather academic and intimidating for the first timer, abstract as well. The book of course is great, however it’s hard to jump into patterns pragmatically just by reading it.


As in my previous post in my concluding paragraph I had said that getting familiar with SOLID principles developed by Robert. C. Martin is great way to get started with principles that will lead the way towards patterns programming later.  Before expanding upon technically on what SOLID is about, I would like to discuss its importance in the whole OO programming space. If you come from a OO language background like Java, C++, C# etc. you already are familiar with Encapsulation, Inheritance, Polymorphism as foundational principles of OO and they are a daily part of your programming life. SOLID takes it one step further, lays out 5 principles that you can apply to re-factor and improve the code making it maintainable, reusable and efficient.


So when you start applying SOLID, you basically are applying some of the fundamental principles on which Design Patterns are developed. SOLID stands for Single Responsibility, Open-Closed principle, Lishkov Substitution principle, Interface Segregation and Dependency Inversion.


If you just take the first two: Single Responsibility and Open-Closed principle, just there you will improve the structure and quality of your classes.


Single Responsibility states: a class should have only a single responsibility.


Say, you are writing a Log class whose job is simply to write messages to different logging mediums. However you also gave it the responsibility of formatting the messages for these mediums, because it’s part of logging function. In addition, you gave it the responsibility of initializing and choosing the medium to log into, for ex: Event logs, Database, Log files etc. So now the Logger class has multiple reasons to change – one is, Write to the log medium, another is formatting the message: perhaps different mediums require different formatting and on top of that initializing the medium . So your class has now grown into one giant monolithic program that has multiple reasons to change – formatting for each medium, initializing the medium and logging to the medium. So if you need to change only one aspect : say change the formatting messages in database , you have to change that class and the rest of the code could possibly break because you needed to make changes for one aspect. We come across situations like this all the time in production code where we change one thing and potentially something else breaks , without us intending it . This sort of programming makes the code not only fragile, but totally un-pluggable.


Ideally in this situation, the Logger class should just take on the responsibility of writing to the medium being free of what medium it is writing to and what formatting that particular medium needs. Although it seems like they are all related functions , they merit to become individual classes based on their specific function and behavior. More so, ideally you should write an interface that can be implemented to write to different log mediums.


public interface ILog

{

void Write(String Message);

}


As you see , when you just take this one principle and follow it while writing the code you will see that you have written classes that are light weight and each is meant to do one particular job – this makes the design pluggable , reusable and efficient  . You can create classes that are specific to a medium – so adding mediums for logging becomes easy later. Also if there is a change required in it , say how you format the message for that medium, you change only the corresponding medium or the formatting class, avoiding the risk of the rest of the code breaking due to the one change you made in one big class.


As you go further and start applying one by one each principle you will see that certain patterns are shaping up, and possibly they can be applied to common scenarios. I guess I will stop here for now, and conclude that the first step is definitely to understand SOLID and start applying it in your programming life seriously.


Below is a great Video on Single Responsibility Principle by Robert C. Martin himself to learn more on it and get started :




We will discuss more on the rest of the SOLID in the upcoming post …until then happy programming.


	


	



			
				


	

	

	

		

						

														
						Development, SDLC, Software Architecture					
									
							

			
			
Technical Knowledge : Breadth and Depth

		

	



	

	
I could have titled this blog “Professional Knowledge : Breadth and Depth “ – however thought that since my blog focuses on a niche readership,  “Technical Knowledge” would sound more appropriate . Anyway, often times at work discussions come up on how mastering a certain subject area leads to growth , especially for technology professionals. Depth plays a key role in technology professions in leading to both job satisfaction and growth. So is depth more important that breadth? I think both are equally important, and they both contribute to an individual’s job performance and satisfaction.


Why Depth?


1) Depth in a subject area establishes you as an expert – the deeper you drill within a subject area focusing on niche fields the better you will do at the design and execution level. Depth is instrumental in achieving high quality results, thus better performance by you as a professional. Say for example , you develop a mastery on ‘Design Patterns’  with regular practice and study – your expertise in that area could play a pivotal role in robust architecture and solid implementation of the architecture which will take the project a long way for years to come.


2) All technical projects / undertakings are team efforts – not individual heroic endeavors. An ‘expert’ in each area of the technical solution will be required to fill the places as opposed to some one who just knows a little bit of all. For example , a software project may have a ‘Single Sign On’ expert just handling the Authentication aspect of the solution where he/she is the ultimate ‘go to’ person  for it. Hence having a niche expertise helps you build your value within  the organization almost always to fill in that spot of your expertise across different projects. A key to job security especially for those who work as consultants.


3) Depth can easily make you a ‘Mentor’ or ‘Leader’ in your area , very important for your own job satisfaction . Let me give you my own example in this case. All along in my career , I made careful choices while consulting – I chose to take up projects which were ‘ASP.Net and C# ‘ centric – this quickly helped me establish myself as a mentor as well as a lead in those areas allowing me to provide expert help and guidance across projects. This leads to great satisfaction , sense of value and achievement.


“Having a niche expertise helps you build your value within  the organization almost always to fill in that spot of your expertise across different projects.”


Why Breadth ?


1) Breadth gives you a vision , an ability to see beyond the purview of a narrow expertise. For example, a business problem can be solved either with a Client Server Architecture or Service Oriented Architecture. If you do not keep up at least with what SOA means , it’s application at a high level , your problem solving abilities are stunted by lack of broader knowledge.


2) If depth establishes you as an expert , breadth can establish you as a sound thinker. A ‘subject matter expert’ may not necessarily be able to lead the overall project , whereas breadth


sound thinker


helps in being a leader and decision maker for the whole project. A typical software project has BAs, QA , Developers, Designers , Project Managers etc. – a professional with a broad understanding of how each works can listen and guide everyone effectively .


3) Breadth just makes you a lot better communicator – it’s easy to communicate in areas where you are deep , however breadth enhances the conversation power many fold because you can quote examples from beyond your forte. A great asset for meetings , hallway brainstorms and white board discussions. This can lead you to opportunities that you want to explore to grow as a professional.


 “Breadth gives you a vision , an ability to see beyond the purview of a narrow expertise.”


The power of knowledge is immense in IT : having both depth and breadth will round you up as a sound professional as well as a leader. Practice gives depth and study can give breadth , combined the result is a highly valued professional.  I always feel in technology you can ‘Read your way up’ –  a small investment in time of may be even an hour a day makes a big difference , it keeps you abreast with the new stuff.  I think if one has the time , if say you work 9 hours day , may be extending it to 10 hours by adding that extra reading time at work itself will better prepare you with your project work in applying and understanding better techniques.