On the Effective Manipulation of Digital Objects Libraries Computer Center Department of Informatics & Telecommunications University of Athens A Prototype-based Instantiation Approach Kostas Saidis, George Pyrounakis, Mara Nikolaidou 9th European Conference on Research and Advanced Technology for Digital Libraries (ECDL 2005)

2 / 32 September 19, ECDL 2005 Outline Motivation – The University of Athens (UoA) DL Digital Objects (DOs) Encoding & Storage Manipulation (DL Application Logic) Manual Handling of DO Type variations Digital Object Prototypes Automatic DO Type conformance Digital Object Dictionary A 3-tier DL Architecture Collection Management & Scope of Prototypes Open Issues & Future Work

3 / 32 September 19, ECDL 2005 The UoA DL Project Over 1 million objects originating from 8 different collections Folklore notebooks, Ancient papyri, Historical archive’s folders & documents, Byzantine music manuscripts, Theatrical photos & brochures, Informatics research papers and dissertations, Medical images, Press articles Heterogeneous & (mostly) digitized material We are developing a Web based DL System for all material, using FEDORA as a digital object repository

4 / 32 September 19, ECDL 2005 Motivation Increase productivity (strict time limits) Simplify & speed up the cataloging process Provide effective Web-based cataloging interfaces (cataloging personnel not librarians) Decrease development time (small team) Avoid custom coding for each content variation Elaborate on reusable and configurable DL modules Treat content variations in a unified manner

5 / 32 September 19, ECDL 2005 Digital Objects A Digital Object is a human generated artifact consisting of the digital content and related information Digital Content (files) Metadata (descriptive, administrative, etc) Structure & Reference information Behaviors (DO related functionality)

6 / 32 September 19, ECDL 2005 Abstract Representation of a DO

7 / 32 September 19, ECDL 2005 Encoding & Storage of DOs Several XML-based standards support various forms of digital content & metadata (METS, FOXML, MPEG21, RDF…) METS Sections, Behaviors, Profiles FEDORA Digital Object Model METS variant in version 1.x Fedora Object XML (FOXML) in 2.x Datastreams, Disseminators, Content Models Focus on how each DO part is encoded & stored

8 / 32 September 19, ECDL 2005 Manipulation of DOs In the context of DL Application Logic, DOs should be manipulated in a higher level of abstraction Focus on the overall behavior of the DO (what are the DO parts and how do they behave) DO Manipulation depends on the nature of the DO – the DO reflects the underlying “real world” object

9 / 32 September 19, ECDL tier DL Architecture

10 / 32 September 19, ECDL 2005 DL Application Logic A DL Module performs the following steps: 1. Loads the DO and its required parts 2. Parses XML and puts the data in the appropriate memory data structures 3. Performs operations on the data 4. Serializes the data in XML format 5. Saves the DO and its parts to the repository Steps 1, 2, 4, 5 require different implementations for each DO Type

11 / 32 September 19, ECDL 2005 DO Types? Do we capture, express and use DO Typing information in an effective manner? METS “Profiles” & FEDORA “Content Models” model DO Types… … but their goal is to be used by humans as a guide and not by the DL System as a DO type specification We resolve DO Typing issues manually

12 / 32 September 19, ECDL 2005 Manual Handling of DO Types Developers generate ad-hoc, custom & not reusable implementations of DO types’ variations of behavior Catalogers carry out manual XML editing in a low level of abstraction with too technical, complex & over detailed semantics DL modules exhibit limited evolution and configuration capabilities (due to scattered code and strong couplings & interdependencies)

Position The DL System should resolve DO Typing issues automatically (in a manner transparent to the DL Application Logic)

14 / 32 September 19, ECDL 2005 An example – Theatrical Collection What is an Album DO? A container of photos accompanied by theatrical play metadata What is a Photo DO? A digital image stored in various formats (e.g high quality, www quality, thumbnail) accompanied by the metadata required for describing the picture How can we make Album and Photo DOs behave as such, automatically?

15 / 32 September 19, ECDL 2005 By Drawing on the notions of OO

16 / 32 September 19, ECDL 2005 The OO Viewpoint In the OO model an object is itself aware of its “nature” and behaves accordingly Objects are conceived as instances of a type, automatically conforming to the type’s definitions & specifications OO types are separate entities (named either classes or prototypes)

17 / 32 September 19, ECDL 2005 Digital Object Prototypes A DO Prototype is a DO Type Specification, a separate entity that defines the DO’s: Constitutional parts – metadata sets, files, structure, etc Private behaviors – DO internal operations such as serializations, validations, assignment of default values, content conversions, etc Public behaviors (behavior schemes) – the DO external interface, consisting of high level operations such as Detail view, Browse View, Edit View, etc

18 / 32 September 19, ECDL 2005 OO Encapsulation

19 / 32 September 19, ECDL 2005 Photo Prototype & Instances

20 / 32 September 19, ECDL 2005 Digital Object Instances The process of generating a DO from a Prototype is called instantiation The resulted object is an instance of the prototype A DO instance automatically conforms to the Prototype’s specifications Stored DOs vs DO instances

21 / 32 September 19, ECDL tier DL Architecture

22 / 32 September 19, ECDL 2005 Digital Object Dictionary The runtime environment in which DO instances and Prototypes operate The DO Dictionary Instantiates a DO based on the prototype specifications (loads & parses XML, assigns default values, etc) Exposes the public behaviors of DOs in a high level, uniform API (for use by DL Modules) Saves the DO instance (serializes data structures in XML, performs validations, etc)

23 / 32 September 19, ECDL tier DL Architecture Separation of Concerns

24 / 32 September 19, ECDL tier DL Architecture Storage Separation of Concerns

25 / 32 September 19, ECDL tier DL Architecture Storage DO Typing & Instantiation Separation of Concerns

26 / 32 September 19, ECDL tier DL Architecture Storage DO Typing & Instantiation Composition of DO behavior Separation of Concerns

27 / 32 September 19, ECDL 2005 DL Application Logic Revisited A DL Module performs the following steps: 1. Acquires the DO Instance do = dictionary.acquireObject(“type”) do = dictionary.acquireObject(“uoadl:1024”) 2. Performs operations on its data do.getMDSet(“DC”).getField(“title”) dictionary.executeBehavior(do, “editView”) 3. Stores the DO in the repository dictionary.saveObject(do)

28 / 32 September 19, ECDL 2005 Scope of Prototypes Should we have global DO Types? Collection-pertinent types: A DO Prototype is defined in the context of a Collection Support fine grained definition of collection specific kinds of material Hierarchical naming scheme for types Theatrical Collection Photo: dl.theatre.photo Medical Collection Photo: dl.medical.photo Avoid type collisions

29 / 32 September 19, ECDL 2005 Album Prototype & Instances

30 / 32 September 19, ECDL 2005 Collection Management DL = Hierarchy of DO instances Collections are also DOs, conforming to the Collection Prototype The DL itself is a DO, representing the “super- collection” (the collection of all the collections) All content is modeled in a unified manner All content can be characterized Easily add new collections & sub-collections Allow the DL designer to work out the details of each collection independently, yet in a uniform manner

31 / 32 September 19, ECDL 2005 DL as a Hierarchy of DO instances

32 / 32 September 19, ECDL 2005 Open Issues & Future Work OO Inheritance for DO Prototypes (e.g the Notebook type derives from the Book type) OO Polymorphism for DO instances (e.g the DO “uoadl:1234” is both a Notebook & a Book) Generalize the notion of behavior schemes & investigate relations with FEDORA behaviors Supply general purpose linking capabilities that exceed structural relations Deliver on schedule…