robert sanderson herbert van de sompel - open annotation · • aligned with trend towards...

Open Annotation: Technical OverviewRobert Sanderson, Herbert Van de Sompel

Robert Sanderson Herbert Van de Sompel

Prototyping TeamResearch Library

Los Alamos National Laboratory

http://www.openannotation.org/

http://groups.google.com/group/oac-discuss

OAC is funded by the Andrew W. Mellon Foundation

Open Annotation: Technical Overview


Outline

• Motivation

• OAC’s Perspective on Annotations

• Design Choices

• Alpha 3 Data Model

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Motivation (1)

• Annotations are a core ingredient of scholarship:

• Transcribe and annotate medieval manuscripts;• Annotate maps with maps;• Annotate video recording of endangered languages with non-

verbal communication events;• Annotate 3D museum artifacts;• Your use cases …

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Motivation (2)

• Existing solutions for scholarly annotation are repository-centric, tied to silos:

• Annotation in terms of specific repository and/or collection, no global scope;

• Only consumable in client/server combination that created the annotation;

• Annotations not shareable beyond original server – can not create cross system services based on (enriched & merged) annotations.

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Open Annotation Collaboration

• Focus on interoperability for annotations in order to allow sharing of annotations across:

• Annotation clients;• Content collections;• Services that leverage annotations.

• Focus on annotation for scholarly purposes. But desire to make the OAC framework more broadly usable.

• In order to gain adoption => tools, communities, integration of scholarly communication with other areas of discourse.

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OAC’s Perspective on Annotations (1)

• The following characterize an annotation:

• There is an author (human, software agent) of an annotation;• The annotation occurs at some point in time;• There is a body of an annotation;• There is a target of an annotation;• The body annotates the target, i.e. the body is somehow

“about” the target.

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• Body and target of an annotation can be of any media type.

• A video can annotate a Web page; a Web page can annotate a video.

• This is contrary to the prevailing view in which the body is textual.

• Annotation, body, and target can have different authors.

• This is contrary to the prevailing view in which annotation and body have same authorship.

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• Most (scholarly) annotations involve parts of resources (image regions, slices of a video, dimensions of a dataset).

• The annotation framework should provide support for resource segment identification and description.

• A variety of more complex annotations involve multiple targets (and maybe multiple bodies?).

• The annotation framework should support this. • So far, no compelling use cases for multiple bodies have been

identified.

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Design Choices (1)

• Interoperability specified in terms of the Architecture of the Web(URI, link, resource, representation, …) , Semantic Technologies, Linked Data.

• Aligned with desire to more tightly embed scholarly communication in overall human discourse;

• Aligned with trend towards machine-actionable scholarly communication system;

• Aligned with approach we followed in other efforts (OAI-ORE for Aggregations; Memento for versioning).

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Design Choices (2)

• Client autonomy.

• Not an annotation protocol (cf. Annotea) but an annotation model combined with a publish/subscribe mechanism;

• No reliance on a server that helps with generation of annotations. Only a server that supports publish/discovery of the annotation created by the client is assumed.

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Protocol

publish, subscribe, consume

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Publish/Subscribe

publish subscribe consume

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Design Choices (3)

• An annotation is an information resource (aka document).

• Earlier versions of the model regarded annotations as conceptual, non-information resources. This approach was related to:• Ideas to model annotations as events;• Ideas to model annotations as OAI-ORE Aggregations.

• Community feedback to this approach was negative:• Added complexity without added value;• The use of OAI-ORE, and especially its Proxies, was deemed

artificial.

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Design Choices (4)

• Significant attention to problems related to the ephemeral nature of the Web.

• Representations of URI-addressable resources change over time, resulting in ambiguous or incorrect annotations, as well as annotations that lack (representations of) body and/or target.

• The approach provides hooks to allow:• Recognizing ambiguous/incorrect annotations, e.g. via timestamp

and fixity for body and target;• Reconstructing the annotation, e.g. via timestamps, scholarly

archives, and Memento.

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Design Choices (5)

• A model that gracefully builds from simple to complex• The simple core of the model supports elementary annotation use

cases.• The model becomes gradually more complex to accommodate

increasingly complex use cases.

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Basic Model

• The basic model has three resources:• Annotation (an RDF document)

• Default: RDF/XML but others via Content Negotiation• Body (the comment or text of the annotation)• Target (the resource the body is about)

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Basic Model Example

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Additional Relationships and Properties

• Any of the resources can have additional information attached, such as creator, date of creation, title, etc.

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Additional Properties Example

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Annotation Types

• There can be further types of Annotation, such as a Reply.• Example: Replies are Annotations on Annotations.

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Annotation Types Example

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Annotation Types Example

We'll come back to these …

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Inline Information

• It is important to be able to have content contained within the Annotation document for reasons of Client Autonomy:

• Clients may be unable to mint new URIs for every resource• Clients may wish to transmit only a single document

• Third parties can generate new URIs if the client does not

• The W3C has a Content in RDF specification that describes how to do this:

• http://www.w3.org/TR/Content-in-RDF10/

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http://www.w3.org/TR/Content-in-RDF10/�


Inline Information: Body

• We introduce a resource identified by a non resolvable URI, such as a UUID URN, as the Body.• We then embed the data within the Annotation document using the 'chars' property from the Content in RDF ontology.

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Inline Body Example

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Multiple Targets

• There are many use cases for multiple targets for an Annotation:• Comparison of two or more resources• Making a statement that applies to all of the resources• Showing the provenance of resources• Making a statement about multiple parts of a resource

• The OAC Data Model allows for multiple targets by simply having more than one hasTarget relationship.

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Multiple Targets Example

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Segments of Resources

• Most annotations are about part of a resource

• Different segments for different media types:

• Text: paragraph, arbitrary span of words• Image: rectangular or arbitrary shaped area• Audio: start and end time points, track name/number• Video: area and time points• Other: slice of a data set, volume in a 3d object, …

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Segments of Resources (2)

• Web Architecture Segmentation:

• A URI with a Fragment identifies part of the resource• Media-specific fragment identifiers; eg XPointer for XML• W3C Media Fragments URI specification for simplesegments of media: http://www.w3.org/TR/media-frags/

• We introduce a method of constraining resources:

• Introduce an approach for arbitrarily complex segments that cannot be expressed using Fragments• Can be applied to Body or Target resource

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http://www.w3.org/TR/media-frags/�


Segments of Resources: Fragment URIs

• URI Fragments are a syntax for creating subsidiary URIs that identify part of the main resource

• The syntax is defined per media type• X/HTML: The named anchor or identified element

• http://www.example.net/foo.html#namedSection

• XML: An XPointer to the element(s)• http://www.example.net/foo.xml#xpointer(/a/b/c)

• PDF: Many options, most relevant two operations:• http://www.example.net/foo.pdf#page=2&viewrect=20,80,50,60

• Plain Text: Either by character position or line position:• http://www.example.net/foo.txt#char=0,10• http://www.example.net/foo.txt#line=1,5

•:30


Segments of Resources: Media Fragments

• Media Fragments allow anyone to create URIs that identify part of an image, audio or video resource.

• The most common case is for rectangular areas of images:• http://www.example.org/image.jpg#xywh=50,100,640,480

• Link to the full resource as well, for all Fragment URIs

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Media Fragments Example

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Media Fragments Example

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Complex Constraints

• The ConstrainedTarget(CT-1) identifies the segment of interest

• The type of description is dependent on the media type and nature of the target resource.

• If a Fragment URI is not possible, we introduce a Constraint to describe the segment of interest

• Media Fragments embed the segment description in the URI• Constraints are entire resources, so can be more expressive• Constraints may also describe 'contextual' information

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Constraint Example

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Inline Information: Constraints

• We can also use inline information in the same way as for the Body resource to include the Constraint data.

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Inline Constraint Example

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RDF Constraints

• Instead of having the information in an external document, it could be within the RDF of the Annotation document.

• We attach information to the Constraint node

• The Annotation Ontology models its "Selectors" in this way

http://code.google.com/p/annotation-ontology/

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RDF Constraint Example

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RDF Constraint plus Media Fragment

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Constrained Body

• The body may also be constrained in the same way as Targets

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Constrained Body

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Annotating a Non-Document

• The Target of an Annotation does not have to be a document: can be a Non Information Resource

• Non Information Resource as Target• Annotations about:

• Concepts• Physical things • Locations • or any other non-document

• Example: A video about a real life painting

• Non Information Resource as Body• We'll come back to this…

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Non Information Resource Example

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Annotations and Time

• Web Resources change over time, but keep the same URI

• This is important for linking, but makes Annotation hard. We need to know when the annotation applies to the resource.

• This is true for Body and Target(s).

• The created time is not sufficient, as the Annotation, Body and Target could be created at different times. The Body could be about a previous state of the Target.

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Web-Centric Annotation: No Persistence

Google Sidewiki Annotation on http://news.bbc.co.uk/ as of 2010-06-14

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Web-Centric Annotation: No Annotations

Archived page from: http://www.dracos.co.uk/work/bbc-news-archive/2010/03/08/07.05.html

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Web-Centric Annotation: Desired Cross-Linking

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Annotations and Time

• There are three different types of Annotation with respect to Time:

• Timeless Annotations• These are always relevant, regardless of the current state of the resource.

• Uniform Annotations• There is a single timestamp at which all of the resources should be considered.

• Varied Annotations• Each of the resources (Body, Targets) should be considered at a different time.

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Timeless Annotations

• The model for a Timeless Annotation is the base model

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Uniform Annotations

• If the same time is applicable to all resources, we attach it to the Annotation using the oac:when predicate.

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Uniform Annotation Example

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Varied Annotations

• If different timestamps are required for each resource, we use oac:when from an oac:TimeConstraint.

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Varied Annotation Example

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http://www.openannotation.org/

http://groups.google.com/group/oac-discuss

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