Feed the Masses

Introducing Vice - Outbound Syndication in Plone via the Zope Component Architecture Paul Bugni Center for Public Health Informatics Feed the Masses T: 206.221.7444 F: 206.616.5249 1100 NE 45 th Street, Ste 405 Seattle, WA 98105 www.cphi.washington.edu

Agenda
Syndication
Vice History and Demonstration
Zope Component Architecture
Vice Integration
Customizing Syndication

What is syndication?

To publish or broadcast
Alternative to browser only audience for publishing content

“Web Feed” or “News Feed”

Data format for frequently updated content

Content distributors syndicate a web feed

Users can easily subscribe to the feed

Simplifies keeping up with changes

Using Aggregators

Prevailing syndication formats
That’s the beauty of standards, there are so many to pick from!

Two prevailing formats (as of mid-2005)
RSS 2.0
Atom 1.0

Exposing the myth of RSS compatibility
“I would like to publicly apologize for my previous misstatements. There are not 7 different and incompatible versions of RSS; there are 9” - Mark Pilgrim[1]
[1] http://diveintomark.org/archives/2004/02/04/incompatible-rss

RSS Stands For?
RDF (Resource Description Framework) Site Summary (RSS 1.0 and RSS 0.90)
Rich Site Summary (RSS 0.91)
Really Simple Syndication (RSS 2.0)

First, there was the mark up language RDF
Resource Description Framework
Used to store metadata (author, language, copyright…) about the content

RSS 0.90
In 1999 Netscape created the standard named RSS version 0.90
The beginning of RSS as we know it today

RSS 0.91 (part 1)
Dan Libby (Netscape) improved 0.90 and released RSS version 0.91

RSS 0.91 (part 2)
Dave Winer (Userland) also created an improvement of RSS 0.90 and called his version 0.91

Confusion ensued
Two versions named RSS 0.91 with different specifications

RSS 1.0
Rael Dornfest (O’Reily) released RSS version 1.0
Based on the RDF standard rather than RSS
RSS 1.0 was therefore incompatible with previous RSS versions

So to clear things up
Userland named their next release version 2.0
Harvard Law accepted responsibility for the RSS 2.0 specification
RSS 2.0 is very similar to 0.9 series (generally compatible)
RSS 1.0 remains very different

RSS 2.0
The specification is copyrighted by Harvard University and is frozen.
The intent is that future work will be done under a different name.

Atom 1.0
In part, motivated by the desire to be free of the RSS confusion

Atompub Working Group

IETF (Internet Engineering Task Force)

The Atom syndication format has been adopted as IETF Proposed Standard RFC 4287

RSS 2.0 versus Atom 1.0
A number of ambiguities exist in RSS 2.0 including:
No required fields (Atom requires title unique id and last updated)
No way to indicate if payload is encoded or plain text (Atom requires explicit declaration and includes options such as another XML vocabulary)
Autodiscover is not standardized and relies on an unregistered MIME type
Only Atom 1.0 is in an XML namespace and has specific guidelines for interpreting extension elements. (RSS 2.0 does not permit well formed XML markup)
http://www.intertwingly.net/wiki/pie/Rss20AndAtom10Compared

Need For Better Syndication in Plone
2006-Feb-01 PLIP #128 was born
PLIP: Plone Improvement Proposal, analogous to python’s PEPs: Python Enhancement Proposal
#128: Pluggable Plone Syndication (PPS)

PLIP #128 Motivation
The current portal_syndication tool [only supports RSS 1.0 format and therefore] doesn’t have support for enclosures

PLIP #128 Motivation (continued)
[No current support to] extend syndication beyond common object attributes (i.e.Title, description, body etc.)

PLIP #128 Motivation (continued)
[No current support for] different types of feed entries for different content types (i.e. enclosures for media content a.k.a. podcasting)

PLIP #128
Enable advanced (RSS 2.0, Atom) site-wide syndication on all ATCT content “out-of-the-box” using Zope 3-based adaptors (via Five) which are extendable beyond ATCT to any content type.
(ATCT : ATContent Types)

Vice to the Rescue!

And the name ?
Before vice, there was “CMFSin”, “basesyndication”, “fatsyndication”, “synz”…
“ Vice was the cleanest name we could come up with.”

Vice was Born at the (now infamous) BBQ Sprint
Participants
Derek Richardson
Liz Dahlstrom
Mikel Larreategi
Jørgen Gårdsted Jørgensen
Paul Bugni

Then Vice Picked up a Sponsor
Derek Richardson (student)
Florian Schulze (mentor)
Report: http://www.openplans.org/projects/vice/google-summer-of-code-report

Vice also benefited from additional sprints
Plone4Artist Multimedia Sprint
2007 Plone Conference Sprint

Installing Vice

Add Vice to the Buildout Eggs
Using buildout, edit buildout.cfg and add vice.plone.outbound to the [eggs] section:
eggs =
elementtree
vice.plone.outbound

Include the Vice Configuration Files (a la zcml slug)
Edit buildout.cfg and add vice.plone.outbound to the [instance] zcml
[instance]
zcml = vice.plone.outbound

That’s It?
Well, it should be, but Zope2 is not yet “eggified” and vice has dependencies related to Zope3 eggs

Workaround:
Add “fake_zope_eggs = true” to the [zope2] section of your buildout

Re-run ./bin/buildout

Install Product in Portal
Install “Outbound Syndication (Vice)”

Configure for Use
From the plone_control_panel (site setup)…
Find the syndication “configlet” listed in the add on product configuration
Enable syndication

Out of the box demo
< break to vice demo >

Design Goals
So which format do we architect around?

Ideally, none of them!

Separation of Concerns
Goal: separate the action of syndication from any particular format

Goal: Make it easy to add additional feed types

Goal: Make it easy to extend beyond common object attributes

How to Manage the Complexity?
Idea: isolate behavior in “objects” dedicated to a single purpose.

The Previous Approach:
Use multiple inheritance to mix and match objects (create mix-ins)
Subclass the mix-ins for further customizations

The Downsides
Complexity: objects built from a large number of base classes
Lack of cohesion: lots of unrelated attributes and methods

A Better Way
Introducing the Zope Component Architecture

Three Core Concepts
Interfaces
Components
Adapters

Interfaces
A formal description of how to interact with an object
Can be as simple as a label, or “marker”

Components
An “object” with introspective interfaces

Adapters
Inexpensive mechanism to add behavior (defined in interfaces) to existing components
Extends a components functionality without modifications to the component

Types of Components
Content Components
View Components
Adapter Components
Utility Components

Zope Component Architecture
Web Component Development with Zope 3, 3rd ed.
Philipp von Weitershausen

Core Vice Concepts
Containers (such as Folders) are “Feedable” (marked with the IFeedable interface, adaptable to the IFeed interface)
Content Objects (such as Documents) are “Feed Items” (adaptable to the IFeedItem interface)

IFeedable
Mark all folders as being “feedable”:
<class class="zope.app.folder.Folder">
<implements interface=".interfaces.IFeedable" />
</class>

IFeed
Represents a “Feed”
Use to adapt objects that can provide items to feed

IFeed
class IFeed(Interface):
"""A syndication feed e.g. RSS, atom, etc. To syndicate a container,
adapt it to IFeed.
"””

IFeed Adapters
Adapted to the Plone Site Root
All Folders (IATFolder)

IFeedItem
Represents a single item, or entry in a feed

IFeedItem
class IFeedItem(Interface):
"""A single syndication feed item.
""”

IFeedItem Adapters
Adapted to the respective AT Content Types:
IATDocument
IATEvent
IATLink
IATImage
IATFile
IATNewsItem

Thus Vice Handles all AT Content Types “out of the box”
This includes any customized ATCT subclasses

How to Syndicate a New Type

New Type Must Be Adaptable to IFeedItem

Register the Adapter Factory

<adapter
factory=".syndication.ExampleDexterityPageFeedItem"
name="vice-default"
trusted="true" />
<class class=".syndication.ExampleDexterityPageFeedItem">
<require
permission="vice.ViewFeeds"
interface="vice.outbound.interfaces.IFeedItem" />
</class>

Define the IFeedItem Adapter Class
class ExampleDexterityPageFeedItem(ExampleDexterityFeedItemBase):
""”Makes example.dexterity.page.IPage IFeedItem adaptable.
"""
implements(IFeedItem)
adapts(IPage, IFeed)
@property
def body(self):
"""See IFeedItem
"""
v = getMultiAdapter((self.context, self.context.REQUEST), Interface, name=u'syndicate_page')
return v().encode('utf-8')

Page Template for Body of Feed Item
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"
xmlns:tal="http://xml.zope.org/namespaces/tal"
xmlns:metal="http://xml.zope.org/namespaces/metal"
xmlns:i18n="http://xml.zope.org/namespaces/i18n"
lang="en"
i18n:domain="plone">
<body>
<p tal:content="context/Description" />
<div tal:content="structure context/body " />
</body>
</html>

That’s It
< break to demo using example.dexterity >

Adding a new Feed Format
This trivial act is left as an exercise for the reader

But there’s a vice sprint going on this weekend!
http://www.openplans.org/projects/plone-conference-2008-dc/vice

Inbound Story?
Ajax approach: plone.syndication.inbound
Persistent approach: feedfeeder
http://plone.org/products/feedfeeder

How to get involved
Did I mention the sprint?
Join the mailing lists:
http://www.openplans.org/projects/vice/lists
Developer list: vice-dev@lists.openplans.org
Discussion list: vice-discussion@lists.openplans.org

Questions?

Feed the Masses

by pbugni on Oct 15, 2008

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Feed the Masses — Presentation Transcript