Eoin Prout

Yes! Regular Expressions are simple once you learn the grammar, and thats also the biggest problem with them, unless you learn the grammar, Regular Expressions look like the gibberish of some dark art, And unless you actually sit down and study you’ll not make much progress with them.

There are some good books on Regular Expressions.
Regular Expression Pocket Reference

Mastering Regular Expressions

Once you have Regular Expressions in your tool box you’ll quickly see many uses they can be put to such as page scraping or data validation, I’ve even seen them used them for updating Delphi code bases to the latest version of Delphi.

In the train timetable service I used 3 Regular expressions to extract the information need to output optimized version of the time table.

The first two

/<input type=”hidden” name=”DepTime” value=”[0-9][0-9]:[0-9][0-9]

/<nput type=”hidden” name=”ArrTime” value=”[0-9][0-9]:[0-9][0-9]

Are used to strip out the table elements which contain the departure and arrival times,
The strings which match the patterns are stored in two arrays, one for arrival and one of departures.

Then iterating through the two arrays a third regular expression is used

[0-9][0-9]:[0-9][0-9]

This Regular Expression returns the times from the strings contained in the two arrays and it is this information which is used to produce the timetables you see when using the service.

I’d be interested to hear an if there is an even easier way to do this.

There is an excellent tool available for working with Regular Expression, Regex Buddy It is a fantastic piece of software.

Most languages and platforms support Regular Expressions, For Delphi you can use the TRegex component which is free, for Delphi .NET it’s not needed as .NET supports Regular Expressions.

When creating the train time table service I decided to use a RESTful approach for the API, This meant the URL should confirm to a number of RESTful Principles.

1) The URL represents a resource and consist of NOUNs, not VERBs.
If you using Verbs then you are not using REST. you’re using RPC.
One of the defining principles of REST is the use of a limited set of Verbs POST,GET,PUT and DELETE which correspond to Create, Read, Update and Delete (CRUD).
This allows the easy contruction of URLS so that a consumer and go directly to the resource required.
for example
http://www.eoinprout.com/trains/Cork/Cobh/
will return the Cork Cobh time table resource.

2) The URL hides implementation details.
There are many advantages to hiding the implementation details not the least of which is that it allows the background implementation to be changed without affecting the API.
In my case the service is implemented in PHP but by using mod_rewrite it was possible to hide the implementation details of the service, One more advantage of this is that many search engines do not properly index dynamic pages which require the correct parameters to be set. This aids the discovery of the service.

3) The service should expose other parts of the service via links allowing discovery and traversal.
The trick here is not expose everything in one URL. In the case of my service the user starts at ../trains/ which presents a list of departure stations and links to a list of possible destinations, from there another link will return the URL for the particular time table required. so all the users needs to remeber is the ../trains/ URL.

4) GETs are used for obtaining a copy of the resource.
GET is the standard HTTP method getting content when you type a URL into the address bar of the browser it is a GET which is executed , On IrishRail.Com POSTs are used to retrieve a copy of the time table a user may be looking for.
There are serious disadvantages when using POSTs to retrieve a resource, The resource cannot be bookmarked, The URL for the resource cannot be sent to someone else, URL cannot be constructed and search engines cannot index the resource.