Etech2005 Atom Tutorial

Building Applications with RSS, Atom, and the Atom API

Ben Hammersley

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Today’s topics•Atom and RSS in the structure of the web

•The Philosophy behind Atom•The Atom Document model and syntax

•The architecture of the Atom API

•Elemental - a simple CMS using Atom and RSS

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1:30 - 3:15

3:45 - 5:00

Version WarningDo Not Deploy!

oh, all right

<entry version="draft-ietf-atompub-format-05: do not deploy"xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-05">

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The context of RSS and Atom

• Syndication formats - describing documents

• RSS 0.9 ➡ 0.91 ➡ 1.0 ➡ 0.92 ➡ 2.0

• RDF

• Separate and parallel development

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The Simplest Possible RSS 2.0 Feed<?xml version="1.0" encoding="utf-8"?><rss version="2.0">

<channel><title>The Simplest Feed</title><link>http://example.org/index.html</link><description>The Simplest Possible RSS 2.0 Feed</description>

<item><description>Simple Simple Simple</description></item>

</channel></rss>

The Simplest Possible RSS 1.0 Feed

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<?xml version="1.0" encoding="UTF-8"?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <channel rdf:about="http://example.org/index.html"> <title>The Simplest Feed</title> <link>http://example.org/index.html</link> <description>The Simplest Possible RSS 1.0 Feed</description> <items> <rdf:Seq> <rdf:li rdf:resource="http://example.org/example_entry" /> </rdf:Seq> </items>

</channel>

<item rdf:about="http://example.org/example_entry"> <title></title> <link>http://example.org/example_entry</link> </item> </rdf:RDF>

The Simplest Possible Atom Feed<?xml version="1.0" encoding="utf-8"?><feed version="draft-ietf-atompub-format-03: do not deploy" xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-03">

<head> <title>The Simplest Feed</title> <link rel="alternate" type="text/html" href="http://example.org/index.html"/> <author><name>Ben Hammersley</name></author> <updated>2004-10-25T15:07:02Z</updated></head>

<entry> <title>The Simplest Entry Document</title> <link rel="alternate" type="text/html" href="http://example.org/example_entry"/> <author><name>Ben Hammersley</name></author> <id>http://example.org/2004/12345679</id> <updated>2004-10-25T15:07:02Z</updated> <content type="TEXT">Simple Simple Simple</content></entry>

</feed>

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RSS 2.0 RSS 1.0 AtomSimple, adhoc,

temporary, loosely defined data, very loosely defined

standard, many many uses

Fantastic for machine readable lists. Useless for anything else.

Complex, strict, pre-planned, strongly

defined data, strongly defined standard,

burdened with evil buzzword. Fantastic

for complex document mining. A nightmare for tiny

ad-hoc apps.

Simple, strictly defined data,

strictly defined standard, with

extra architectural

loving

Current Atom Users

• Lots of weblogs - Blogger especially

• Flickr

Back to the Greeks

Democritus - 460BC

“Nothing exists except atoms and empty space - everything else is

opinion.”

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Wittgenstein

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The world consists of independent atomic facts out of which

larger facts are built

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• What it is called

• Who created it

• When it was created

• What it contains

• Where it is

All the machine can know about a resource

All other metadata is secondary, subjective and human added

• What it is called

• Who created it

• When it was created

• What it contains

• Where it is

CategoryLocationLanguage

Referencesetc.

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Key Concept

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An Atom Document explicitly states the minimum we can know about the resource and no less.

Principle of the

conservation of metadata

The Simplest Possible Atom Feed<?xml version="1.0" encoding="utf-8"?><feed version="draft-ietf-atompub-format-03: do not deploy" xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-03">



</feed>

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Lost once, lost forever

You can’t bring metadata back, once it’s gone, without introducing doubt.

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RSS 2.0 Lost Data<?xml version="1.0" encoding="utf-8"?><rss version="2.0">

<channel><title>The Simplest Feed</title><link>http://example.org/index.html</link><description>The Simplest Possible RSS 2.0 Feed</description>

<item><description>Simple Simple Simple</description></item>

</channel></rss>

Date?

Author?

URI?

Key Concept

It’s ok to have a lossy representation - RSS, HTML, whatever - but the resource itself must conserve the data.

Data Entropy Cannot Be Reversed.

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Nothing lost in Atom<?xml version="1.0" encoding="utf-8"?><feed version="draft-ietf-atompub-format-03: do not deploy" xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-03">



</feed>

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• Atom Entry Document

• Atom Feed Document

Two types of Atom document

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An Atom Entry Document<entry version="draft-ietf-atompub-format-05: do not deploy"xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-05">

<title>First entry document</title><link rel="alternate" type="text/html" href="http://ben-hammersleys-computer.local./~ben/Etech%202005/Elemental/atom2html.cgi?atom=1110228064.atom"/><author><name>Ben Hammersley</name></author><id>http://ben-hammersleys-computer.local./~ben/Etech%202005/Elemental/1110228064.atom</id><updated>2005-03-07T20:41:04Z</updated><content type="TEXT">This is the content of the first entry document.</content>

</entry>

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Reusable Syntax of Constructs

• Text

• Person

• Date

• Link

• Category

• Identity

• Service

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Links, Content

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• link rels

• content payloads

• content pointers

Atom Feeds

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The Elegant Feed

• An Atom feed is a collection of documents, topped with its own metadata.

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Atom Feed - Who, what, where, when, and what again.

<?xml version="1.0" encoding="utf-8"?><feed version="draft-ietf-atompub-format-03: do not deploy" xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-03">



</feed>

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Creating a feed

• Slice - choose a view

• Dice - take the namespaces out

• Mash - Stick them together

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Key Concept

A Feed is the representation of a Query over Resources

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Atom Documents, Revision.

• An Atom Document contains at least the minimum that can be said about a resource, whether an Entry or a Feed.

• An Atom Feed contains the Atom Entry documents resulting from a Query over resources. It’s a type of resource in itself.

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The Atom API

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APIs through the ages

• BloggerAPI, Metaweblog API

• XML-RPC or SOAP

• For the manipulation of resources: REST

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First Principles • HTTP has verbs - GET POST PUT DELETE

• Representations of Resources

• GET the HTML representation of the resource

Erk!

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GET

Application CONTENT

Ask for content from the

application, by asking for a

specific URI over a specific Encoding.

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POST

ApplicationCONTENT

Send content to a listening

application, which creates the

resources, and returns the one thing we don’t know already.

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PUT

ApplicationCONTENT

Send content to a listening

application, which REPLACES a

resource.

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DELETE

ApplicationDIE! KILL! DIE!

Tells the listening application, to destroy the resource.

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Manipulating a resource

• Full control means stating all of the data we know

• Hence, we’re stating (most) of an Atom Entry document

• Anything we don’t know is returned to us, along with the result code.

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Key Concept

An Atom API call is an Atom Entry Document over an HTTP verb.

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• Endpoints

• Authentication

So what else do we need to know?

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• PostURI - one per system

• EditURI - one per resource

• FeedURI - one per query

• ResourcePostURI - one per system

Endpoints

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PostURI<link rel="service.post" type="application/atom+xml" href="PostURI" title="The sitename." />

POST an Atom Entry to it.

One or more representations are created. Atom, HTML, etc.

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EditURI<link rel="service.edit" type="application/atom+xml " href="EditURI" title="Readable desc of the entry." />

The client GETs the representation which is formatted as an Atom entry. The client may then update the entry and then PUT it back to the same URI. The PUT will cause all the related resources to be updated, for example, the HTML representation.

A client will send a DELETE to the EditURI to delete an entry.

The EditURI is unique to the resource.

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FeedURI<link rel="service.feed" type="application/atom+xml" href="URI goes here" title="The name of the query." />

The Client GETs a FeedURI to receive an Atom feed of the representation of the query.

You’ve already built this loads of times. Nice.

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ResourcePostURI

For posting of binary data.

<link rel="resource.post" href="URI for Resource Posting goes here" title="The name of the site.">

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Other features• Features defer to their elders

• Security, Caching, Encryption

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After the break

• Documentcentrism

• Using the Atom API to create an application

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Documentcentrism

ContentStored

asAtomEntries

Input View

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The System of the World

Atom Entry Document

Atom Feed XHTML RSS PDF

Atom API File creation Other interfaces

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Why represent in Atom

• Because it’s a demo :-)

• Because Atom itself is just a representation

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Elemental

• Input as an HTML Form

• Store as Atom Entry Documents

• Two outputs - Atom Feed, HTML document

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Download Elemental

http://benhammersley.com/speaking/EmergingTech2005/Elemental.tgz

Stepping through the code

Extending Elemental

• More inputs

• More outputs

• Use Apache and Content Negotiation

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Using Atom yourself

• http://atomenabled.org

• http://www.intertwingly.net/wiki/pie/FrontPage

• “Developing feeds with RSS and Atom”

Thank you

Technology

Etech2005 Atom Tutorial