Assertion.ru

Sometimes all this terms seem quite confusing. Or it’s better to say they usually or even always do. Especially when different people and companies understand the situation around them in different ways. So let’s start from the very beginning.

There are lots of specifications or standards around us. Webster dictionary describes standard as something established by authority, custom, or general consent as a model or example. So basically it is the list of rules, which others while using have to obey.

Let’s create a computer language. First of all the specification is needed, that will describe the whole concept model, tell developers what can be written as a program, how it will behave, what will be compiled, executed and etc. After creating all these necessary documents – that’s it, one can stop right there. If the idea is good enough several other companies might want to create their implementations: f.e. compilers and executing environments. But they must obey the specification. Otherwise the same programs will run on one and run differently or even fail on the other implementation. Fulfillment by an implementation of all specified requirements is called conformance.

Why is it so important? Well, let’s say this new language was used to create a program for stock exchange. Imagine it was written in the US, well tested and used at NYSE. It was so good, that other countries all over the world bought a license and started using it on their implementation of this new language. If an implementation didn’t obey the spec, the same program might do different things with clients’ money. Basically this stock exchange program might sell when commercial agent pushed the “buy” button, or buy steel instead of fruit.

The good question could be: “Why different implementations? Let’s create one and use it.”. There are different answers. Several companies might want to use this language on different platforms (Solaris, Linux, Windows) and devices (desktop, mobile phone, PDA, student calculator, etc). Others want to optimize algorithms for their needs, f.e. implement them so the big database program will be 10 times faster.

The key point is that several different implementations must work exactly the same and according to the spec. If they do so they are called compatible. The bad part is that no one can be sure. That is why the verification mechanism is needed. Usually it is a test suite that verifies the conformance and compatibility. And in this case it is wrong to say that something is almost compatible or 99% compatible. There could be either yes or no.

Let’s move towards an example. Sun Microsystems invented Java language. To be more precise several versions of Java for different markets were created. The most famous are Java ME, Java SE and Java EE. And for each of them there is a separate specification. Sun Microsystems has its own implementation, which is most commonly used. However the language is so good, that there are quite a few other companies and their implementations. For compatibility and conformance purposes there are TCKs (Test Conformance Kit). TCK is a product that includes a number of tests, which check if an implementation is correct according to the rules from specification.

My intend was to give an idea of what specification, conformance, compatibility and TCK are and why they are so important.