This is the Title of the Book, eMatter Edition
Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.
Chapter 11: REST: Representational State Transfer
Submit a purchase order
Update or cancel a purchase order
O’Reilly also wants to enable their authors to:
Add and update author biographical information
For internal purposes, O’Reilly also wants to enable their editors and designers to:
Create or update a cover for the book
The next step is to consider how these services can be implemented in a REST style.
Modeling Resources
Before you can model resources, you must create a domain model, which describes
entities and their relationships and provides the information necessary for resource
modelling (see Figure 11-2).
Based on this domain model, it is possible to model the resources and design URIs to
access them. The web service makes available a specific URL to represent a books list
resource, for example, /books/.
The absolute URL for this resource may look like, but
because the hostname and protocol will not change, there is no need to include them
in the examples.
Note that the process the web service uses to generate the response is completely
transparent to the client. A list of books may be available as a physical document or
may be created by the server side application at run-time. All the client has to do is
submit a request, and a document containing the book list is returned.
Figure 11-2. Book service domain model
This is the Title of the Book, eMatter Edition
Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.
Programming REST
The XML document that a client receives may look like this:
<?xml version="1.0"?>
<Books xmlns=""
<Book id="progwebsoap" xlink:href="progwebsoap/">
<Title>Programming Web Services with SOAP</Title>
<Authors xlink:href="progwebsoap/authors/"/>
<Book id="progxmlrpc" xlink:href="progxmlrpc/">
<Title>Programming Web Services with XML-RPC</Title>
<Authors xlink:href="progxmlrpc/authors/"/>
There are several important things to notice. XML is only one of the possible repre-
sentations that a client may receive as a result of content negotiation (which will be
discussed later). The example also includes
xlink:href attributes that point to the
resources that contain related information (book and author details in this case).
This is a key feature of REST. A client changes its state by accessing the alternative
resources addressed by URLs in response document.
An xlink:href attribute is described in XLink specification that defines
an attribute-based syntax for attaching links to XML documents. The
most current version of the XLink specification can be found at http://
Note that, even though the server can make these URLs absolute (/books/progweb-
soap/ or even, for now it is kept relative.
The benefit of doing this will be clearer when discussing the “cover page” service.
The model can use the ISBN (as Amazon does, for example) instead of using unique
book identifier (as O’Reilly does), but it wouldn’t change anything in this design and
It is important to decide what information to include in this representation and what
to keep for subsequent requests. It was decided to present
Title, ISBN, and ListPrice
elements and provide links to other resources. While it is possible to include all rele-
vant information, it’s not always feasible or practical. For example, book informa-
tion may include a cover page; author information may include the author’s bio and
pictures as well as links to articles. There is no reason to include all this information
in the book list, so the line must be drawn somewhere.
At this stage, the server has implemented a service that returns a list of books. Work
can now focus on the service that returns specific information about a particular
book. This service will be available through the URL /books/progwebsoap/.

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