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APPROACHES TO MACHINE-
ACTIONABLE LINKS: A
HYPERMEDIA FORMAT FOR DATA
Breakout session
ESIP Summer Meeting, 2013-07-12
Chapel Hill, North Carolina
Stephen M Richard, organizer

Objectives
 Develop a content model for information
associated with links
 Enable hypermedia applications
 Focus on functionality related to data discovery,
evaluation, access, and processing
 Review usage of links in web architecture
 Look at example use scenarios
 Proposal for content

‘Traditional’ Web application
HTML is the hypermedia format
Application state is directed by a Human
<ul class="secondary">
<li><a href="http://www.nytimes.com/pages/automobiles/index.html">Autos</a></li>
<li><a href="http://www.nytimes.com/ref/topnews/blog-index.html">Blogs</a></li>
<li><a href="http://www.nytimes.com/pages/books/index.html">Books</a></li>
<li><a href="http://wordplay.blogs.nytimes.com/cartoons/">Cartoons</a></li>
<li><a
href="http://www.nytimes.com/ref/classifieds/?incamp=hpclassifiedsnav">Classifieds</a></li>
<li><a href="http://www.nytimes.com/crosswords/index.html">Crosswords</a></li><li
id="navWorld"><a href="http://www.nytimes.com/pages/world/index.html">World</a></li>
<li id="navUS"><a href="http://www.nytimes.com/pages/national/index.html">U.S.</a></li>
<li id="navPolitics"><a href="http://www.nytimes.com/pages/politics/index.html">Politics</a></li>
<li id="navNYRegion"><a href="http://www.nytimes.com/pages/nyregion/index.html">New
York</a></li>
<li id="navBusiness"><a
href="http://www.nytimes.com/pages/business/index.html">Business</a></li>
<li id="navDealbook"><a href="http://dealbook.nytimes.com">Dealbook</a></li>
<li id="navTechnology"><a
href="http://www.nytimes.com/pages/technology/index.html">Technology</a></li>
<li id="navSports"><a href="http://www.nytimes.com/pages/sports/index.html">Sports</a></li>
<a href="http://www.nytimes.com/ref/
topnews/blog-index.html">Blogs</a>

Distributed applications on
the Web
 HTTP as the transport for application
messaging
 Operations: GET, PUT, POST, DELETE
 Agnostic about message format and content
 Headers provide metadata for messages
 Language, MIME type

Richardson Maturity Model
http://martinfowler.com/articles/richardsonMaturityModel.html
Tunneling, RPC
(Plain Old XML)
Operate on
domain objects
Use HTTP operations
as intended
HATEOAS (Hypertext As
The EngineOf Application
State)
NOTE: Roy Fielding has made is clear that level 3 RMM is a pre-condition of REST.
Useful comparison table: http://nordsc.com/ext/classification_of_http_based_apis.html

Approaches to application messaging
 Tunneling
 HTTP GET or POST
 URL or message content contains method request
 SOAP, ‘remote procedure call’
 encode methods and parameters in URLS
 HTTP messages always directed to a single web
location

Tunneling RPC call
 http://api.flickr.com/services/rest/?
method=flickr.test.echo&name=value
 http method is GET
 https://sdb.amazonaws.com/?
Action=PutAttributes&other parameters…
 http method is POST
 URI contains action
 Message semantics depend on action .

 Object based
 Define resource scheme for application objects
 Use HTTP request to create, read, update, delete
 Various representations may be available for the
objects

Resource object-based
 https://api.twitter.com/1.1/
statuses/mentions_timeline.json
 http://resources.usgin.org/uri-gin/
nmbgmr/bhintercept/API:30-035-2024
 specific schema used is only known to
client and server

URI template
 A sequence of characters for describing a
range of URIs through variable expansion
(IETF RFC-6570)
 Example: Get scientific metadata for a
dataOne data package
 https://datadryad.org/mn/object/{identifier}
 identifier:= "http://dx.doi.org/10.5061/dryad.8790"
 https://datadryad.org/mn/object/http://dx.doi
.org/10.5061/dryad.8790

 Hypermedia
 messages specify resources and possible actions
(read, write, create, delete, filter, report, etc.)
 controls provided to invoke next action
 media format must be understood a priori by
client applications
 server can change any URI except the initial entry
point

Machine Actionable Links
 Essential to hypermedia applications
 HTML
 <a> anchor element for HTTP GET
 <form> form element for HTTP POST
 <img>

Can we produce a content
model for hypermedia
controls for data
applications?

Scenarios
 Examine several scenarios commonly
encounter with data access and processing
 Search and data access
 Linked data
 Web processing services
 Vocabulary usage in content

Hypermedia search
 Search catalog
 Get list of distributions
 SelectWMS distribution
 Add to arc map project

CI_OnlineResource affordance
Distribution options offered by an ISO19139 XML metadata response
<URL> http://services.kgs...service=WMS
<protocol> OGC:WMS
<name> Service Description
<description>WMS Capabilities
<function> webService
<URL> http://services.kgs.ku.....;service=WFS</URL>
<protocol> OGC:WFS
<description>WFSCapabilities
<URL> http://services.kgs.ku..../MapServer
<protocol> ESRI
<description> ESRI Service End Point
<URL> http://repository.stategeothermaldata.org/..._20121212.zip
<name> Zipped 2007 Excel file containing BoreholeTemperature data for the State of Kansas
<function> download

Hypermedia and linked data
 Offer an ‘affordances’ representation for any
URI
 Dereference URI to see list of things can do
with it
 Picture, text explanation, searches,
discussion, usage, plot, publications, people,
brokers…
 Over to Doug…

Web processing service
1. Landing page: start process
1. Select existing and execute
2. Start new—identify inputs and parameters and
execute
2. Successful completion
1. Modify parameter and rerun
2. Save results
3. Visualize result
 If process is largely user driven, HTML forms
provide necessary hypermedia

Semantics: Vocabulary
 URI identifies a concept
 Hypermedia helps user understand concept
 Hypermedia to help machine agent navigate
semantic web
 Related, broader, narrower
 RDF graph, SPARQL endpoints
 ISO codelists, GML codeType

Vocabulary examples
 <gsmlem:lithology
 xlink:href="http://resource.geosciml.org/classifier/
cgi/lithology/wacke"
 xlink:title="Wacke" />
 gmd:CI_RoleCode
 codeList="http://www.isotc211.org/2005/resources/
Codelist/gmxCodelists.xml#CI_RoleCode"
 codeListValue="pointOfContact">
 pointOfContact</gmd:CI_RoleCode>

Survey
Specification Link
ATOM http://tools.ietf.org/html/rfc4287
CoRE http://tools.ietf.org/html/rfc6690
ESIP discovery http://wiki.esipfed.org/index.php/Discovery_Change_Proposal-8
GML codeType
HAL http://tools.ietf.org/html/draft-kelly-json-hal
Home document http://tools.ietf.org/html/draft-nottingham-json-home
Hydra http://www.markus-lanthaler.com/hydra/spec/latest/core/
IANA link type registry
IETF Web Linking http://tools.ietf.org/html/rfc5988
ISO19115/19139 see USGIN profile document
RDFa http://rdfa.info/about/
xlink http://www.w3.org/TR/xlink11/
OWC offering OCG 12-080 Table 3

Content model for link
 link (syn: href, targetURI)
 title
 type
 rel
 overlayAPI
 template
 profile

Link property
 Essential– must be a URI that will dereference
using web architecture (DNS,TCP/IP), with
result according to other link properties
 Typically using http
 URI syntax (IETF RFC-3986) specifies that
"each URI begins with a scheme name"
[RFC3986, section 1.1.1]

Title
 Text string that identifies the link function for
a human user.
 Only necessary if link is being used for human
user interaction

type
 Registered string that identifies the media
type
 MIME type (http://www.iana.org/assignments/media-types).
 Allow comma-delimited list
 Intention is that if a type is listed here, it is
known to be available from the host

rel property
 Semantics of link
 Attribute value is list;
 Use global vocabulary for interoperability
(IETF RFC-5988)
 include one of the 5 original Atom link@rel
values
 Domain specific rel values should be URI that
will dereference as a vocabulary term

overlayAPI: Legacy approaches
 identifies the API for messages tunneled to a
component on the target server
 should be defined by the service specification
for the protocol or service type
 Include version information if applicable

template: guidance for URI
patterns
 identifies template scheme
 if a value is provided for this attribute, the
targetURI MUST be interpreted as a template
 service specification should define the URI
that identifies the scheme and version.

profile property
 application specific conventions
 Specific vocabularies for message content
 Restrictions on alternate usages of interchange
format schema
 May apply to template scheme or overlayAPI

parameters
 Additional parameters encoded as key-value
pairs
 Account for information like layer name in
WMS, feature Name inWFS or ESRI service,
coverage name inWCS
 Can this be done more simply?

Other possible properties
Property Scope
altTitle Title value in a different character set, or
language
behavior list of properties specifying behavior expected in
client when link is actuated
descriptionURL URL that locates a detailed text description of
what the online resource is/does
hints profile-specific information about link operation;
granular to protocol or overlayAPI method level
hreflang language of resource content; multiple
"hreflang" parameters indicate options
length advisory size linked content in octets

Where to from here
 Collect examples of example links intended
for machine to machine operation
 (examples from white paper)
 What vocabularies are necessary?
https://github.com/usgin/usginspecs/blob/master/
MetadataAsHypermediaApp.docx
ESIP Google Doc or Discovery Cluster
Presentation to ESIP Semantic Cluster

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