Atom and Web Atom and Web MappingMapping

Atom and Web Atom and Web MappingMapping

Charlie Savage

MapBuzz, Inc.

Charlie Savage

MapBuzz, Inc.

Slides at http://blog.mapbuzz.com/

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Atom Will Change MappingAtom Will Change Mapping

Atom is a better platform for exchanging geospatial data then existing standards

By “Atom” I mean both the syndication format and publishing protocol

Atom offers a surprisingly deep platform well suited for building web applications

We're witnessing the birth of the next great technology standard

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Exchanging Geospatial DataExchanging Geospatial Data

Its fairly easy to share maps on the web – Google, Microsoft, Yahoo, WMS

But what about other geospatial information – features, events, histories, etc?

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What do We Need?What do We Need?

A standard identification system

A standard interaction protocol

Standard data exchange formats

Standard way of handling state

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How Does the Web Do It?How Does the Web Do It?

Identification system – URIs

Interaction protocol - HTTP

Formats - xhtml, png, jpeg, etc.

State – session state is embedded in formats (xhtml) via links

Let’s clients and servers evolve independently

“Engineer for Serendipity” – Roy Fielding

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Web Feature Server (WFS)Web Feature Server (WFS)

An Open Geospatial Consortium (OGC) standard

Lets clients view, query, lock, create, update and delete features

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WFS Is Deeply Flawed for the WebWFS Is Deeply Flawed for the Web

Identification – Features do not have URIs

Interaction – Uses a proprietary API (GetCapabilities, GetFeature, etc.)

Format – uses GML

State – GML supports links (via XLink), but it is rarely used

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GML Is Moderately Flawed for the WebGML Is Moderately Flawed for the Web

GML was not designed for the web – it was designed for the Enterprise

GML requires the creation of custom schemas - which is great for the Enterprise and terrible for the Web

Theoretically everyone could agree on a single GML profile such as the Simple Feature Profile

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WFS/GML Will Fail on the WebWFS/GML Will Fail on the Web

No URIs means no linking, page rank, etc

Proprietary interface requires custom clients that are tightly coupled to servers

Incorrect use of HTTP as a transport protocol throws away the benefits of the web infrastructure (caching, load balancing)

Lack of common GML schema causes information to be segregated by organization, industry type, problem domain

No serendipity – how many WFS mashups do you see?

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Enter Atom – Built for the WebEnter Atom – Built for the Web

Identification – everything has a URI

Interaction – Specified by Atom Publishing Protocol, based on HTTP

Formats – Atom syndication format, service documents, category documents

State - Full support for linking and therefore session state

Fully utilizes web infrastructure

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Atom SyndicationAtom Syndication

Defines a small set of the most useful attributes, such as name, published date, etc.

Direct overlay with the Dublin Core attributes

Applicable to many problem domains

Extensible through XML namespaces

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Atom Publication Protocol (APP)Atom Publication Protocol (APP)

APP = Atom + REST

Application protocol that defines how clients and servers interact

Deftly leverages HTTP: Uses GET, POST, PUT and DELETE

Uses HTTP response codes for error handling

Enables HTTP caching mechanisms

Built in support for arbitrary media types – locations, pictures, podcasts, etc.

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A Simple Data ModelA Simple Data Model

Image courtesy of Dave JohnsonImage courtesy of Dave Johnson

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Built-in AggregationBuilt-in Aggregation<feed>

<title>Search items</title>

<entry>

<title>Victoria - Foss4G Conference</title>

<source>

<title>Maps</title>

<app:collection href=“…“/>

</source>

</entry>

</feed>

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ExtensibleExtensible

GeoRss – Locations

Feed Paging and Archiving – retrieve subset of entries

Threading – Comments and discussions

Atom Ranking Extensions – Any type of ordering information such as user ratings

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Amazing UptakeAmazing Uptake

Browser support - Opera, Firefox, Internet Explorer

Corporate support – Microsoft, Google, Amazon, SixApart, MapBuzz (Facebook, LinkedIn, MySpace next?)

OpenSource support – OpenLayers, Lucene, Apache Abdera

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A Great Web Service PlatformA Great Web Service Platform

Atom syndication provides a base level of understanding across problem domains

Atom publishing protocol makes it easy to build REST base services

Its much easier to extend Atom then start from scratch

Atom will become the lingua franca of web services

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Using Atom to Replace WFSUsing Atom to Replace WFS

Simple - Atom + GeoRss

Complex - Atom + GML

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Atom + GeoRssAtom + GeoRss

Simple, grass roots standard, for specifying location

Advantages Easy to implement Indexed by Google Covers a large number of applications

Disadvantages Not all atom attributes are applicable No custom attributes No topology, measurements, coverages

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Atom + GeoRss ExampleAtom + GeoRss Example

<entry>

<title>Brown Palace Hotel</title>

<georss:point>39.7 -104.9</georss:point>

</entry>

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Atom + GMLAtom + GML

Advantages Custom attributes

Disadvantages Harder to implement

Not indexed by Google

Very limited client support

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Atom + GML ExampleAtom + GML Example

Let’s find an example of Simple Feature Profile

Google around…hmmm…where are they?

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What About Queries (Filters)?What About Queries (Filters)?

OGC Filter Specification defines spatial query language

Difficult to use with GET Need to URL encode xml request

GET query length limited by Internet Explorer

Often used with POST but this is WRONG: Breaks linkability

Breaks cacheability

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Query ExampleQuery Example

http://localhost:8080/geoserver/wfs? request=getfeature& service=wfs& version=1.0.0& typename=states& filter=<ogc:Filter xmlns:ogc="http://ogc.org" xmlns:gml="http://www.opengis.net/gml"> <ogc:BBOX> <ogc:PropertyName>the_geom</ogc:PropertyName> <gml:Box srsName="http://www.opengis.net/gml/srs/epsg.xml"> <gml:coordinates>-73.99312376470733,40.76203427979042 -73.9239210030026,40.80129519821393</gml:coordinates> </gml:Box> </ogc:BBOX> </ogc:Filter>

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Queries Are ResourcesQueries Are Resources

Treat queries as resources – they become “part of the web”

Create, update, delete queries via Atom of course (treat the queries as a media resource)

Neatly solves the GET/POST dilemma

Makes it possible to track the number of times a query is executed, total amount of time, etc.

Also allows queries to be reused across servers (probably of dubious value, but…)

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Open IssuesOpen Issues

Custom attributes – is GML going to play in this area – if so what profile?

Multiple flavors of GeoRss

Minor – non-applicable Atom attributes (author, title, category, updated)?

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Reaching ConsensusReaching Consensus

OGC has finally noticed REST – just starting to talk about “RESTifying” WFS and other standards

OGC is a standards organization – most likely won’t move quickly

OGC’s focuses on the traditional GIS market and large organizations so expect membership pushback

In the meantime, join us on the GEO-REST discussion group where we talk about these issues

Participate in our next interoperability day where we make sure our clients and servers really work together