(4) Precious Snowflakes

• Many applications are not as unique as you might think
  • reusing design patterns and even technologies is a good idea
  • avoiding reuse usually should be justified by good reasons
• Take the Web's HTML as an inspiring example
  • HTML is not all that great as a document format
  • it was good enough as a container for a lot of useful content
  • the network effect far outweighs its functional shortcomings
• Simplicity and wide applicability are valuable
  • simplicity means a lower barrier to entry
  • wide applicability means higher chances to create network effects

(5) Location-Based Services (LBS)

• Location is an important facet in many settings
  • accessing information about location-sensitive
  • accessing information from a certain location
• Mobile computing has a big impact on the LBS landscape
• Vertical vs. horizontal integration of services
  • most LBS models nowadays are built as vertical applications
  • horizontal integration improves mashability and reuse
• Services on the Web should focus on providing information
  • using the Web as an application platform (building apps)
  • using the Web as an information platform (publishing data)

(6) Location and the Web

• How to expose location as a Web-level concept
  • metadata/semantics about location information (GeoRSS [http://georss.org/])
  • location as a resource (Geo URI [http://tools.ietf.org/html/rfc5870] geo:48.198847,16.369704 [geo:48.198847,16.369704])
  • location as part of interaction semantics (location negotiation in HTTP)
• Location and the Web (LocWeb) Workshops
  • LocWeb 2008 [http://medien.informatik.uni-oldenburg.de/LocWeb2008/] at WWW2008 (DBLP [http://www.informatik.uni-trier.de/~ley/db/conf/www/locweb2008.html])
  • LocWeb 2009 [http://ifgi.uni-muenster.de/archives/locweb2009/] at CHI 2009 (DBLP [http://www.informatik.uni-trier.de/~ley/db/conf/www/locweb2009.html])

(7) Uniform LBS Interface

(8) Feeds!

• Information dissemination is a complex and varied problem
• Feeds look at all these problems with a simple approach
  • the simple approach lacks some sophistication/specialization
  • less specialization means wider applicability
  • wider applicability means bigger network effects
  • pull-based syndication is loosely coupled and scalable
• Some claim that pull publishing is bad and Publish/Subscribe (PubSub) is good
  • scalable PubSub is expensive to implement (but still may make sense)
  • PubSubHubbub (PuSH) [http://code.google.com/p/pubsubhubbub/] implements feed-based PubSub

(10) Tiling the Planet

• Location is a great key into services
• Tiling schemes are convenient and scale well
  • map imagery routinely is served as a tiled service
  • tiling allows back-end and intermediary optimization
• Datasets most often are dumped onto the map as a whole
  • works well for small dataset and capable networks/devices
  • breaks down for big datasets and constrained environments
  • regionated KML is a solution but has no interaction protocol

(11) Quadtree-Based Tiling and Addressing Scheme

(12) RESTifying Tiles

• Tiles are resources REST's sense of thing of interest
  • each tile represents the collection of location-based information resources
  • tiles have a logical name (0230102122) and relationships
• Linking tiles allows LBS clients to navigate through the tile space
  • navigation is possible in all four directions or up and down
  • the tile space wraps around at the west/east borders
  • the tile space ends at the north/south borders

(13) Tile 0230102122

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns:fh="http://purl.org/syndication/history/1.0" xml:lang="en-US" xmlns="http://www.w3.org/2005/Atom">
 <id>http://tiledfeeds.yimingliu.com/amtraks/0230102122.xml</id>
 <link type="text/html" href="0230102122.html" rel="alternate"/>
 <link type="application/atom+xml" href="http://tiledfeeds.yimingliu.com/amtraks/0230102122.xml" rel="self"/>
 <title type="text">Tile 0230102122</title>
 <updated>2010-07-08T00:40:07-07:00</updated>
 <author>
  <name>TileFeed Generator</name>
 </author>
 <link href="query_schema.xml" rel="query-schema"/>
 <link type="application/vnd.google-earth.kml+xml" href="0230102122.kml" rel="alternate"/>
 <link href="0230102120.xml" rel="north"/>
 <link href="0230102300.xml" rel="south"/>
 <link href="0230102123.xml" rel="east"/>
 <link href="0230102033.xml" rel="west"/>
 <link href="023010212.xml" rel="up"/>
 <link href="02301021220.xml" rel="down-northwest"/>
 <link href="02301021221.xml" rel="down-northeast"/>
 <link href="02301021222.xml" rel="down-southwest"/>
 <link href="02301021223.xml" rel="down-southeast"/>
 <fh:complete/>
 <entry>
  <id>http://localhost:3000/items/345</id>
  <link type="text/html" href="http://localhost:3000/items/345" rel="alternate"/>
  <title>BKY</title>
  <updated>2010-07-08T00:40:07-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>BKY</name>
     <description>University Ave. and Third St.</description>
     <Point>
      <coordinates>-122.299994999871,37.8676030004272</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/111</id>
  <link type="text/html" href="http://localhost:3000/items/111" rel="alternate"/>
  <title>EMY</title>
  <updated>2010-07-08T00:40:07-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>EMY</name>
     <description>5885 Horton Street</description>
     <Point>
      <coordinates>-122.290680000357,37.8406790003872</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/509</id>
  <link type="text/html" href="http://localhost:3000/items/509" rel="alternate"/>
  <title>OAC</title>
  <updated>2010-07-08T00:40:07-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>OAC</name>
     <description>700 73rd Avenue</description>
     <Point>
      <coordinates>-122.197740496936,37.7518812571236</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/515</id>
  <link type="text/html" href="http://localhost:3000/items/515" rel="alternate"/>
  <title>OKJ</title>
  <updated>2010-07-08T00:40:07-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>OKJ</name>
     <description>245 Second Street</description>
     <Point>
      <coordinates>-122.270743999583,37.79464699997</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
</feed>

(14) Tile 023010212 (Zoom Out)

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns:fh="http://purl.org/syndication/history/1.0" xml:lang="en-US" xmlns="http://www.w3.org/2005/Atom">
 <id>http://tiledfeeds.yimingliu.com/amtraks/023010212.xml</id>
 <link type="text/html" href="023010212.html" rel="alternate"/>
 <link type="application/atom+xml" href="http://tiledfeeds.yimingliu.com/amtraks/023010212.xml" rel="self"/>
 <title type="text">Tile 023010212</title>
 <updated>2010-07-08T00:40:56-07:00</updated>
 <author>
  <name>TileFeed Generator</name>
 </author>
 <link href="query_schema.xml" rel="query-schema"/>
 <link type="application/vnd.google-earth.kml+xml" href="023010212.kml" rel="alternate"/>
 <link href="023010210.xml" rel="north"/>
 <link href="023010230.xml" rel="south"/>
 <link href="023010213.xml" rel="east"/>
 <link href="023010203.xml" rel="west"/>
 <link href="02301021.xml" rel="up"/>
 <link href="0230102120.xml" rel="down-northwest"/>
 <link href="0230102121.xml" rel="down-northeast"/>
 <link href="0230102122.xml" rel="down-southwest"/>
 <link href="0230102123.xml" rel="down-southeast"/>
 <fh:complete/>
 <entry>
  <id>http://localhost:3000/items/287</id>
  <link type="text/html" href="http://localhost:3000/items/287" rel="alternate"/>
  <title>ACA</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>ACA</name>
     <description>100 I Street</description>
     <Point>
      <coordinates>-121.815132000194,38.0180849997628</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/330</id>
  <link type="text/html" href="http://localhost:3000/items/330" rel="alternate"/>
  <title>BCI</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>BCI</name>
     <description>Military West St at West 2nd St</description>
     <Point>
      <coordinates>-122.157481059365,38.0544916599225</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/345</id>
  <link type="text/html" href="http://localhost:3000/items/345" rel="alternate"/>
  <title>BKY</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>BKY</name>
     <description>University Ave. and Third St.</description>
     <Point>
      <coordinates>-122.299994999871,37.8676030004272</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/111</id>
  <link type="text/html" href="http://localhost:3000/items/111" rel="alternate"/>
  <title>EMY</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>EMY</name>
     <description>5885 Horton Street</description>
     <Point>
      <coordinates>-122.290680000357,37.8406790003872</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/836</id>
  <link type="text/html" href="http://localhost:3000/items/836" rel="alternate"/>
  <title>FFD</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>FFD</name>
     <description>2000 Cadenasso Drive</description>
     <Point>
      <coordinates>-122.066106110976,38.2479950002171</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/467</id>
  <link type="text/html" href="http://localhost:3000/items/467" rel="alternate"/>
  <title>MTZ</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>MTZ</name>
     <description>601 Marina Vista Ave.</description>
     <Point>
      <coordinates>-122.136353000047,38.0197330001869</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/509</id>
  <link type="text/html" href="http://localhost:3000/items/509" rel="alternate"/>
  <title>OAC</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>OAC</name>
     <description>700 73rd Avenue</description>
     <Point>
      <coordinates>-122.197740496936,37.7518812571236</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/515</id>
  <link type="text/html" href="http://localhost:3000/items/515" rel="alternate"/>
  <title>OKJ</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>OKJ</name>
     <description>245 Second Street</description>
     <Point>
      <coordinates>-122.270743999583,37.79464699997</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/715</id>
  <link type="text/html" href="http://localhost:3000/items/715" rel="alternate"/>
  <title>SUI</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>SUI</name>
     <description>177 Main Street</description>
     <Point>
      <coordinates>-122.039542999873,38.2434650000423</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/758</id>
  <link type="text/html" href="http://localhost:3000/items/758" rel="alternate"/>
  <title>VAL</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>VAL</name>
     <description>4355 Sonoma Blvd.</description>
     <Point>
      <coordinates>-122.256222815849,38.1329822662137</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
 <entry>
  <id>http://localhost:3000/items/762</id>
  <link type="text/html" href="http://localhost:3000/items/762" rel="alternate"/>
  <title>VMW</title>
  <updated>2010-07-08T00:40:56-07:00</updated>
  <content type="application/vnd.google-earth.kml+xml">
   <kml xmlns="http://www.opengis.net/kml/2.2">
    <Placemark>
     <name>VMW</name>
     <description>Highway 37 and Fairgrounds Drive</description>
     <Point>
      <coordinates>-122.227942999716,38.134326999961</coordinates>
     </Point>
    </Placemark>
   </kml>
  </content>
 </entry>
</feed>

(15) Location-Based Content

• Feed entries carry content in KML [http://de.wikipedia.org/wiki/Keyhole_Markup_Language]
  • KML is a big bag of features (whatever Google Earth can do nowadays)
  • tiled feeds may only carry a subset of standardized KML 2.2 [http://code.google.com/apis/kml/documentation/kmlreference.html]
• Services are free to use smart back-end methods
  • clustering can be use to aggregate entries into compound entries
• Adding entries is supported using the Atom Publishing Protocol (AtomPub) [http://tools.ietf.org/html/rfc5023]
  • clients can POST/PUT/DELETE entries to a tiled feed
  • most services probably handle write access through the root feed

(16) Paged Feeds

• LBS are free to decide how many entries they include in a feed
  • as soon as pages are used, ranking/sorting becomes an issue
  • 10-20 is a typical number for regular feeds on the Web
  • additional information can be exposed in paged feeds
  • paged feeds add more depth to a tile
• Paged feeds are necessary for larger information sources
  • they allow incremental rendering of tiled feeds
  • mobile clients might choose to not load additional pages

(17) iOS Tiled Feed Client

(19) What do you want to GET today?

• Advanced LBS may provide query capabilities
  • getting only a subset of the entries in the result feed
  • queryability has a big impact on caching and scalability
• Exposing query parameters as a property of a tiled feed
  • feeds provide queryability introspection
  • similar to the approach of HTML forms (but not using HTML)
  • clients are able to understand an LBS's queryability
• Feed querying is independent of tiled feeds
  • the goal is to produce two orthogonal RESTful designs

(20) Faceted Search

• Combining the two most popular search paradigms
  • direct search that uses one-step querying and ranked results
  • navigational search that allows users to explore structured information spaces
• Faceted search supports iterative search procedures
  • incrementally narrowing down the search to relevant hits
  • facets are presented so that users can use the best distinguishing features
• Faceted search can be regarded as an extension to querying
  • faceted search services add hints to the available query parameters
• Faceted search is relatively expensive to implement

(21) Faceted Search Example

(23) Exposing LBS as Tiled Feeds

(24) Feed Mashups

• Reading multiple feeds from multiple services
  • combining entries is easy because all entries are the same
• Feed mashups can be built as services
  • consume and republish tiled feeds
  • mobile clients consume aggregate feeds instead of individual feeds
  • feed sets can be consumed across various clients

(25) From Pull to Push

• PubSubHubbub (PuSH) builds a push model on top of Feeds
  • clients subscribe to feeds by registering a callback URI
  • PuSH hubs notify subscribers by POSTing to the callback URI
  • PuSH hubs are allowed to aggregate notifications for the same callback
• Combining tiled feeds and PuSH implements location-based notifications
  • clients can subscribe to various tiled feeds using the same callback
  • hubs then push all notifications as efficiently as possible
• Some platform have predefined/prescribed push architectures
  • iOS has a push service built into the platform
  • a tiled feed aggregator consumes PuSH notifications and generates iOS push
  • if the push platform does not allow fat pings, entry URIs can be pushed