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Archive for the ‘software architecture’ Category

July 22nd, 2011 by Vivek Khurana

Introducing Krivah

For past some time I have been working on numerous “Enterprise” application. What I noticed that most of them have same bunch of problems. In majority of cases you have some data and bunch of rules to be applied on the data. When I explored this a bit I came to a list of features that I will like to have in a business management framework. Here is the initial list I came up

– Define data easily. By “easily” I mean that a Business user should be able to define data (preferably visually) or modify existing data.
– Pull data from various sources and define a collective business object.
– Define rules with a drag and drop interface.
– Define workflows.
– Define presentation of data.
– Package bunch of features as components and mix components to create applications (SCA)
– Allow individual applications to be stored on separate nodes (hardware) so that you can scale individual applications depending on demand.At the same time whole application should be available to user in a single interface, seamlessly.
– Reporting
– Incremental development of applications and components.

Since I had some free time today, I decided to start writing a framework which meets above requirements. The framework is called Krivah and is based on clojure. The code repo is available at https://github.com/vivekkhurana/krivah . Please note, at the time of writing this post, Krivah is pre-pre-alpha!. The code is for developers only. (not for faint hearted! :) )
Right now nothing special is working. Just a basic entity framework for defining entities. Current code supports only NoSQL and is based on MongoDB. But support for other database is coming soon.

Why Clojure
Clojure is a dialect of lisp that runs in JVM or .Net CLR. Lisp is a language that I find most suitable for business applications. The ability to treat code as data is a blessing for defining business rules. One can use older program source code and pass it to new function, making wrapping functions and extending functions a breeze.

What Krivah is not?
Krivah is not a generic framework. It is focused on business applications and workflow based applications to be precise. So you cannot expect to see Krivah used to build a social networking site. But expect things like inventory management, production planning etc.
To cut down on speculations, I am not trying to build SAP or anything similar. I dont think, this framework will be used by anyone beyond SME.

What is in the name?
Krivah (pronounced Kree-waah) is formed by joining two Sanskrit words Kree meaning work and Vaha meaning flow. Since one of the main focus on this framework will be business workflow, joining Kree and Vaha will mean workflow. :)

Why announcement in pre-pre-alpha ?

Its Friday night here in India and I have whole weekend. I think by Monday morning I should be able to finish couple of task and by sometime mid-next week have something usable by end-user. Since the project is going to be open source, the sooner you release the project, the better it is. :)

So stay tuned for more updates… :)

July 5th, 2009 by Vivek Khurana

Scalable application architectures – stability

Recently I started working on an application that will have to cater to the needs of thousands of users. It is not just the number of users but the application needs to aggregate data from multiple web services and push data to multiple webservice. This might sound as a simple but when you have to talk to about 30 webservice which have nothing in common except the HTTP and XML. Each webservice represents data in different format even though most of them deal with a simple text document. This means we need to figure out a way to create the business object from multiple sources at the same time keep the application linear. The complexity of the requirements increases by leaps and bounds when you have to work with live data. Yup, live up to date data. So the only way out seems to be to have a stateless, asynchronous design. But it is not easy to write stateless asynchronous applications :(

You may argue that why am I worried about the scalability of the application. Let the design evolve over a time. My experience with building applications is that, you cannot have a scalable design that “evolves”.  Not without tons of hard work later and not without breaking few things.  Writing scalable applications is like building an earthquake resistant skyscrapper. You cannot wait for the earthquake to come before you will start working on making the building earthquake resistant. You have to design it up front and test the model in lab before you lay the foundation stone of the building.

So what exactly is scalable. The sad part of computer industry is, we still dont have a scale to measure the scalability. What works for one set of data may fail for another set of data. A friend of mine suggested that, he measures his application profitability if the cost per transaction is less than the revenue per transaction.  I think the logical way to measure scalability would be, to measure how far the application can scale while keeping cost per transaction lower than the revenue per transaction :)

So lets try to define stability. To  an end user stability means that the system is available and capable of doing transaction irrespective load.  So first we need to identify what hampers system availability.

  1. Sudden surge of requests (like being slashdotted)
  2. Large number of requests being received continuous  over a period of time.
  3. Internal problems like memory leaks.

For point 1 we do have a solution. Do a load testing. That should give you an indication how long the system will survive before crashing under the load of sudden surge of request or in short what category of earthquake can building handle.

What about point number 2 ? How do you test a system under large number of continuous requests ? Do you do load testing for couple of days before releasing a new build in production ? One may argue that given the way most internet companies work, you have release the work very often. Acceptable point, but what is the use of adding that on cool new feature, that your marketing guy wants like anything, without testing the system stability ? If your cool new feature crashes it is only going to shake users confidence. To handle the point number 2, you need to test your application under different load conditions continuously for few days. I remember building a stock market ticker which would pass all the tests in development but crash in production. We found later that when the application was in productopn for 3 days continuously, some parts of application suffered from data overflow. Though it might sound a stupid mistake from a developer but the fact is the company suffered considerable losses due to repeatedly crashing application. And this was in the era when stock ticker from webservices was a new feature on the internet and every business head of a financial site, wanted to have the feature on the site because some competitor had it.

Testing for longevity of application is a very important test that is ignored more often than it is conducted. A test for longevity can bring out bugs in application that will go untraced in any other type of testing. The test of longevity needs to handle different load conditions under different time. It is equally important to measure the performance of the application during night conditions (low load) to peak conditions (day time).  Performance of different systems as the application load ramps up or down could reveal certain startling facts about your application.

What about point number 3 ? It takes some experience to identify internal problems. For instance memory leak can only be identified by seasoned programmer as compared to a johnny. So code review plays an important part here.  But what ever you do, some or the other internal problem will arise.  You need to build safety nets for such situations. Like building air bags for front passengers which inflate automatically when the car is hit.  Such impact absorbers will be able to handle internal problems and yet let the system perform or what is known as fault tolerance.

So keeping above points in mind, I have started designing the application. Currently I am evaluating whether to use a RDBMS or go with no-sql. Will post about the same when I arrive to a decision :) .

More later…

February 26th, 2009 by Vivek Khurana

A rose by any other name will end up as a cabbage

Last night a friend of mine pointed me to the 97 things wiki and an interesting axiom “A rose by any other name will end up as a cabbage“. The axiom page talked about how you should name the components in a software project. The idea arises from a simple argument “If you don’t know what it is to be called you don’t know what it is”.

In my opinion natural languages are the best tools for describing the requirements of a project.  Although diagrams are very helpful in explaining the overall logic or flow, but the details of the requirement should always be explained in natural language such as plain English. When requirements are written in plain English, you can toss the requirements across users for comments and get feedback at an early stage of software development. Not all users can understand the complexities of state machines, use case diagrams, ER diagrams etc. but all of them  understand, jargon free simple English. Yes, you can use any other natural language than English, when working with non-English speaking population.

Another advantage of using a natural language to describe requirement is that you get a natural abstraction layer called ‘name’. When you name something you try to come up with a mental abstraction based on the major characteristics of a (physical) object and second time you have to refer to same object or collection of characteristics you call it by a name, instead of long description of the object.  When you see a repeating pattern, give that a name. When you see a bunch of instructions to be executed repeatedly give it a name. When you see an interface, give it a name. At the same time ensure that the name is specific enough to convey the characteristics (eg. cheap,fast,easy, strong etc.) of the abstraction or object. A name that is not specific enough points to lack of clarity in the abstraction layer and is a sign of either too much of abstraction in the system or over engineering. At the same time you need not build abstraction only when you see lots of features being clubbed. An interface might implement only two or three features but the frequency of repetition of those features will make them as a candidate for abstraction and thus a name.

Creating abstraction comes natural to all the humans and it is easy for us to identify things by a name. May be that is why we came up with an idea of commands to computers because it was easier for a human to remember a single command instead of typing a set of instructions to see a list of files in a directory for example.  We further progressed into creating scripts which would be a collection of commands (essentially an abstraction), giving name to a script and then remembering the name as a command.

When you are designing a new software, having a specific name for a component will create the abstraction automatically.  But do watch out if you have too many names in your requirements, you might be suffering from over engineering and you might have created too many abstractions…

Who says whats in the name ?