Sunday, 31 March 2013

ANTLR 4.0

If you do use Google Analytics, you may have noticed that, the API is available for developers to use. Also, on a Youtube video showing "Google Analytics End to End", the engineers show 2 ways that developers can interact with Google Analytics. One is through an API that Google has exposed for developers to use. The second is a small edit box where you can type in the metrics / filters and you click on a button and you get the results based on the filters you mentioned.

Typing things in an English like question / expression which is not exactly sql but, will get you the results you are looking for does come in handy especially since, ordinary users can interface with your system easily. This is conceptually same as the Interactive Shop Finder in malls except that, you type in the question you are looking for. Users will be able to relate to this kind of interface as they will be able to test drive your software. 

Considering that, you need to cook up an expression / question that you will take from the user, parse that and get the results; means you need a small language that will allow your users to express themselves. This may have you filters as pre-defined keywords. For example, ga.City = Pasadena and ga.Country = USA is similar to what Google gives you. 

ANother Tool for Language Recognition will allow you to specify the Backus Naur Form of your small language and build you a parser. So all you have to do is;

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1) Use ANTLR to specify the BNF of your small language
2) Get the parser for your language using ANTLR.
3) Use the parser to parse the user question
4) Catch the elements in the question that makes sense to you. i.e walk the expression tree. This is possible by assigning labels to your grammar rules. This is extremely helpful when you are walking the tree.
5) Build the real query that your database takes and get the result.



References:

ANTLR website has a lot of examples, and the BNF of the mainstream languages like Java and the like. So developers can hit the ground running designing their own small languages.
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