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| − | __NOTOC__== DBRS Design ==
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| − | The term REST - <b>RE</b>presentational <b>S</b>tate <b>T</b>ransfer - was introduced and defined in 2000 by [http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm Roy Fielding in his doctoral dissertation] (Fielding is one of the principal authors of the HTTP v1.1 spec). Conforming to Fielding's architecture is referred to as being <b><i>RESTful</i></b>. A RESTful web service (also called a RESTful [http://en.wikipedia.org/wiki/Web_API web API]) is implemented using HTTP and the principles of REST, with emphasis on the following aspects:
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| − | # definition of URIs for <b>all</b> resources exposed by the web service: e.g. <nowiki>http://example.com/resources/</nowiki><b><i>car</i></b>
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| − | # use of Internet media types for on-the-wire representation. This is often JSON or XML, but can be any valid Internet media type.
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| − | # use of the HTTP v1.1 operations: POST, GET, PUT, and DELETE<sup>1</sup> - [http://en.wikipedia.org/wiki/Create%2C_read%2C_update_and_delete analogous to the database semantics of CRUD: <b>C</b>reate, <b>R</b>etrieve, <b>U</b>pdate and <b>D</b>elete].
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| − | # use of hyperlinks to interact-with and navigate-to resources.
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| − | <sup>1</sup> optional operations such as <tt>TRACE, OPTIONS</tt>, etc. rarely used .
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| − | ==== RESTful URI Design Principles ====
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| − | A URI <tt>domainname/[contextual key(s)]/[resource name]/?[query args and modifiers]</tt> should be structured as follows:
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| − | # must represent a unique object, permanently: if it becomes necessary to relocate a resource, use the response code <tt>HTTP 301 (redirect)</tt> so that the client can find where the resource has been moved to.
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| − | # should be succinct and easy-to-understand: <tt>/some/resource/about</tt> is preferred over <tt>/some/resource/about-acme-corp</tt>.
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| − | # the structure should be consistent: once the strategy is chosen, follow it. As in 1), if the strategy changes, return <tt>HTTP 301</tt> so that users familiar with resources under the previous structure can find them under the new structure.
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| − | # principle-of-least-surprise: URIs should be structured so that they are intelligibly 'hackable' - e.g. if <tt>/events/2010/01</tt> shows a monthly calendar for events from January 2010, then it follows that:
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| − | #: <tt>/events/2009/01</tt> - should show an events calendar for January 2009
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| − | #: <tt>/events/2010</tt> - should show events for the entire year of 2010
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| − | #: <tt>/events/2010/01/21</tt> - should show the events for January 21st, 2010
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| − | # URIs should be composed of keywords that are important to the context of the resource. Typical contextual keys describe:
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| − | #: a resource's type
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| − | #: a resource's category or parent category
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| − | #: key resource data (i.e. the date posted)<div style="line-height:125%"><br/></div>Typically, a URI specifies a categorization that moves from general to specific, e.g. a descending hierarchy like year -> month -> day
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| − | # should not contain any markers that would allow someone to infer (correctly or otherwise!) what sort of underlying implementation technology is being used. Suffixes such as <tt>.php</tt> or <tt>.aspx</tt> should not be used.
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| − | # a URI should be lowercase up to the [resource name] - query args and modifiers can be mixed case. In addition, query args and modifiers change only the <b><i>view</i></b> presented for a resource, <b>never</b> its underlying representation. For example a chart service may show some rows from a database; a query modifier may indicate that the chart should be rendered as a PDF file instead of a PNG image - the presence of the query modifier should in no way alter the information contained in the rows.
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| − | # a URI that refers to a list of resources should use plural nouns; a URI that refers to a single resource should use singular nouns:
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| − | #:: GET <tt><nowiki>http://example.com/myproject/entities/employees</nowiki></tt> - returns a list of employees
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| − | #:: GET <tt><nowiki>http://example.com/myproject/entities/employees/count</nowiki></tt> - returns a count of the list of employees
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| − | #:: GET <tt><nowiki>http://example.com/myproject/entities/employee/1</nowiki></tt> - returns the employee identified in the database with primary key 1
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| − | # Pagination of returned lists of resources is supposed to be managed via HTTP header attributes called HTTP Ranges. Unfortunately, this requires returning response code <tt>HTTP 206 (Partial Content)</tt> which is not universally accepted by clients. Thus, pagination is typically accomplished by appending query modifiers to indicate page number and size:
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| − | #:: GET <tt><nowiki>http://example.com/myproject/entities/employees/?pgNum=0&pgSize=40</nowiki></tt> - returns the first group of 40 employees
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| − | #:: GET <tt><nowiki>http://example.com/myproject/entities/employees/?pgNum=1&pgSize=20</nowiki></tt> - returns the next group of 20 employees
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| − | To protect the server from 'greedy' clients that try to query the entire database, use the response code <tt>HTTP 413 (Request Entity Too Large)</tt> if necessary. The Entity tag (ETag) header, when used with <tt>Last-Modified/If-None-Modified/If-Modified-Since</tt> headers, is very useful in handling the <b><i>Lost Edit</i></b> problem when editing resources selected from partial paginated lists.
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| − | The DBRS utility builds an in-memory representation of the required meta-data for the <b><tt>employee</tt></b> entity to be mapped to the database via a JPA entity and mapped to any RESTful clients via JAXB (supporting both XML and JSON media representations). Initially the back-end generation will target EclipseLink JPA/JAXB + Jersey (1.9.1 at the time of this writing).
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