Datasheet

Regular expressions are a very powerful tool, and there’s much more to them than can be covered in a

brief introduction such as this. You’ll be using them in various places in this book, often within PHP. The

PHP web site has a handy description of regular expression pattern syntax at

http://www.php.net/

manual/en/reference.pcre.pattern.syntax.php

REST

REST, or Representational State Transfer, is a term that is often misused. Strictly speaking, REST describes

an architectural approach to building software systems. The term REST was first used by Roy Fielding,

one of the principal authors of the HTTP specification, in his PhD dissertation: “Representational State

Transfer is intended to evoke an image of how a well-designed Web application behaves: a network of

web pages (a virtual state-machine), where the user progresses through an application by selecting links

(state transitions), resulting in the next page (representing the next state of the application) being trans-

ferred to the user and rendered for their use.”

A web application built on REST principles would model each object stored in the system as a unique

URL. So, a bookstore might use URLs of the following form:

http://www.somebookstore.com/books/0470097744

Here, 0470097744 is the ISBN of the book in question. When the URL is accessed, a document repre-

senting the book is returned— on the web, this is most likely an HTML page. Of course, there isn’t really

a different HTML page for every single book in the store— the pages are all dynamically generated

based on the information passed in the URL.

The HTML page for the book might include a link to a list of reviews of the book:

http://www.somebookstore.com/books/0470097744/reviews

Each review would also have its own URL:

http://www.somebookstore.com/books/0470097744/reviews/1

Each time the user follows a link to new URL, the new URL contains all of the context required to service

the request— there is no state required to be stored on the server; it is stored entirely in the URL. This is

a key feature of a REST system.

In the Web 2.0 world, the term REST is also often used to refer to any simple HTTP interface that exchanges

information (usually XML) without the aid of an additional messaging layer such as SOAP (see the follow-

ing section). The Flickr API has such a REST interface, which is covered in detail in Chapter 4.

REST interfaces such as the one offered by Flickr are URL-based, and represent a very concise way of

sending a request to the remote system. A typical REST request URL might look something like this:

http://www.flickr.com/services/rest/?method=flickr.photos.search

&user_id=50317659@N00&per_page=6&api_key=1f2811827f3284b3aa12f7bbb7792b8d

This URL performs a search for a user’s recent photos on Flickr. Don’t worry about the details of what

all those parameters mean right now — we’ll look at this request in more detail in Chapter 4. You can

Chapter 1: Rewriting the Web

05_097748 ch01.qxp 12/14/06 5:53 PM Page 19