CS 502: Computing Methods for Digital Libraries

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CS 502 Computing Methods for Digital Libraries

• Lecture 22
• Repositories

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Administration
Final examination May 19, 2000 100 - 230pm
Phillips 219 5 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 email if you might wish to take it.
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Administration
Discussion class, Wednesday April 19 One
class only, from 730 to 830 p.m. Online survey
http//create.hci.cornell.edu/cssurvey.cfm
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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.
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Requirements 1
Information hiding Internal organization
should be hidden from client computers.
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Repository layers and interfaces
Persistent Store
Store API
Object Management Layer
Shell API
Interface
External Interface
Clients
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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.

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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.

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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

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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

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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

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Repository systems
Core Repository
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Repository systems
Core Repository
Load Services
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Repository systems
Core Repository
Presentation Services
Load Services
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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

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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)

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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.

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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

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Repository layers and interfaces
Persistent Store
Store API
Object Management Layer
Shell API
RAP Interface
RAP Interface
RAP Command
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Client and repository architectures
Store
End Client
Digital Object Processing
Object Persistence
Object Management
Object Management
Client
Repository
RAP Interface
RAP Interface
RAP Requests
RAP Replies
ORB
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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.