1 CS 502: Computing Methods for Digital Libraries Lecture 22 Repositories

2 Administration Final examination May 19, :00 - 2:30pm Phillips or 6 questions on whole course Do you want an open laptop examination? There will be a make up examination near the beginning of the examination period. Please send me if you might wish to take it.

3 Administration Discussion class, Wednesday April 19 One class only, from 7:30 to 8:30 p.m. Online survey

4 Repositories Definitions A repository is any computer system whose primary function is to store digital material for use in a library. An archive is a repository that is organized to emphasize the long- term preservation of information.

5 Requirements 1 Information hiding Internal organization should be hidden from client computers.

6 Repository layers and interfaces Interface Persistent Store Object Management Layer External Interface Shell API Store API Clients

7 Requirements 2 Object models Support for a flexible range of object models. Few restrictions on data, metadata, external links, and internal relationships. New categories of information do not require fundamental changes to other aspects of the digital library.

8 Multiple disseminations Client can access a choice of forms of digital object: Format -- PDF or HTML Performance -- 8 bit/pixel or 24 bit/pixel color Content -- thumbnail, medium-resolution, high-resolution Repository might store alternative disseminations or derive them when requested.

9 Dynamic content Dissemination is produced by executing code at time client makes request Real-time sensor, e.g., traffic camera, satellite picture User characteristics, e.g., location, user profile Dissemination is intrinsically dynamic, e.g., simulation virtual reality computer program Java applet

10 Metadata Metadata can be linked to digital object: external catalog or index embedded in the digital object generated at run time Granularity of metadata collection of digital objects digital object element of digital object

11 Requirements 3 Open protocols and formats Clients use well-defined protocols, data types, and formats. Architecture must allow incremental changes of protocols. Access management Allow a broad set of policies All levels of granularity Prepared for future developments. Reliability and performance Very large volumes of data Absolutely reliable in retention of data Good performance

12 Repository systems Core Repository

13 Repository systems Core Repository Load Services

14 Repository systems Core Repository Load Services Presentation Services

15 Common repository systems Web server File-based object model plus hyperlinks Good tools for access Weak on long-term preservation Relational database Table-based object model -- schema and data dictionary Good tools for data management Used for long-term preservation in data processing

16 Dumb and smart objects Smart repositories objects behaviors provided by the repository e.g., relational database Smart clients behaviors provided by the client e.g., web server Smart objects repository is very simple digital objects provide their own behaviors compare with object-oriented programming (data + code)

17 Example: CNRI repository Dumb repository for access to digital objects All information stored as typed data in digital objects. A single digital object has both data and metadata. Identification of digital objects is by location independent, persistent URNs. Access controls built into methods for accessing digital object.

18 Repository Access Protocol (RAP) RAP is a simple protocol with two main groups of commands: Deposit digital object Verify digital object Delete digital object Edit digital object Access digital object Access metadata

19 Repository layers and interfaces RAP Interface Persistent Store Object Management Layer RAP Interface Shell API Store API RAP Command

20 Client and repository architectures RAP Interface Object Management Digital Object Processing RAP Interface Object Management Object Persistence ORB Store End Client RAP Requests RAP Replies ClientRepository

21 Components Hardware Repository: Sun Sparc with Solaris or IBM RS/6000 with AIX. Software Communications: CORBA/IIOP distributed object system. Repository shell and object management layer: CORBA and Python. Persistent store: Unix file system, Oracle, Shore. Client: CGI scripts, Java applets.