Transcript Web Services and Fedora - University of Virginia

Web Services and Fedora
Tim Sigmon
University of Virginia
EDUCAUSE Mid-Atlantic Regional Conference
January 14, 2003
What Are Web Services?
• WWW mainly used for human interaction
– HTML forms and HTTP transport
• Web Services are meant to support
machine-to-machine or application-toapplication interaction
Web Services Definition
A Web Service is a unit of application logic providing data
and services to other applications. Applications access
Web Services via ubiquitous Web protocols and data
formats such as HTTP, XML, and SOAP, with no need to
worry about how each Web Service is implemented.
-Microsoft
Another Definition
A Web Service is a software component that is
platform and implementation independent and that
can be:
• Described using a service description language
• Published to a registry of services
• Discovered through a standard mechanism
• Invoked through a declared API
• Composed with other services
- Building Web Services with Java
Web Services Technologies
• XML is the common language
– platform independent
– easy to parse
– human readable (sort of!)
– extensible via namespaces and schemas
• SOAP for transport of information
• WSDL for description of services
• UDDI for discovery
SOAP
• Simple Object Access Protocol
• XML-based messaging
framework
• Transport is usually
HTTP, but can be any
transport
WSDL
• Web Services Definition Language
• XML language for defining Web Services
endpoints, access protocol, service
interface, and implementation details
• Web Services equivalent of an IDL
• Enables automatic generation of language
specific API for accessing a particular Web
Service
UDDI
• Universal Description, Discovery, and
Integration
• Discovery protocol for Web Services
through which applications and/or Web
Services can find other Web Services
• Publish, find, and bind information about
how to use Web Services
• Public registries exist but UDDI can also
be used internally
• UDDI has been slow to catch on
Additional Web Services
Technologies
• WS Choreography
– a language to compose and describe the
relationships between Web services (e.g.,
sequencing, state management, etc.)
– ability to combine simple services to produce
complex results
• WS Security
– many areas and standards
• WS Transactions
Web Services Characteristics
• Evolutionary, not revolutionary
• Builds on existing web technologies and
infrastructure
• Still evolving rapidly – numerous standards
initiatives with more appearing almost monthly
(W3C, OASIS, IBM, Microsoft, Sun, …)
• Tools maturing (Apache, IBM, BEA, Sun,
Microsoft, many others)
• Lots of testing the water
• Some highly visible Internet applications
(Amazon, Google)
• Enterprise implementations are emerging
• Tons of hype, including significant over-hype
Some Early Adopters
• Google and Amazon
– http://www.google.com/apis
– http://www.amazon.com/apis
• US Military – logistics applications
between branches of the service (e.g.,
provisioning cargo planes)
• According to Forrester, 52% of US
companies > $1B have rolled out or are
rolling out a Web Services project
Fedora
This Fedora Project is not the
Redhat Fedora project.
The Fedora Project
• Fedora Digital Object Repository System
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Extensible digital object model
Repository System exposed via Web Service APIs
Scalable, persistent storage for content and metadata
Local and remote content
Associate services with objects
Content versioning
• Fedora Use cases
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Content Management (CMS)
Digital Library architecture
Digital Asset Management
Institutional Repository
Scholarly publishing
Preservation
• Open source software
Fedora History
• Research (1997-present) :
– DARPA and NSF-funded research project at Cornell
(Carl Lagoze and Sandy Payette)
– Reference implementation developed at Cornell
• First Application (1999-2001) :
– University of Virginia digital library prototype
(Thornton Staples and Ross Wayland)
– Scale/stress testing for 10,000,000 objects
• Open Source Software (2002-present):
– Andrew W. Mellon Foundation granted Virginia and Cornell
$1 million to develop a production-quality Fedora system
– Fedora 1.0 released in May 2003
– www.fedora.info
Digital Object Model
Architectural View
Persistent ID (PID)
Disseminators
System Metadata
Globally unique persistent id
Public view: access methods
for obtaining “disseminations”
of digital object content
Internal view: metadata
necessary to manage the object
Datastreams
Protected view: content
that makes up the “basis”
of the object
Digital Object Model
Example Disseminators
Persistent ID (PID)
Disseminators
Get Profile
List Items
Get Item
List Methods
Get DC Record
Default
Simple Image
System Metadata
Datastreams
Get Thumbnail
Get Medium
Get High
Get VeryHigh
Fedora and Web Services
• Fedora Repository is a set of Web Services
– Access/Search (API-A) and Management (API-M)
– Service descriptions published using WSDL
– Both SOAP and REST bindings
• Back-end services
– Digital object behaviors implemented as linkages to
other distributed web services
– Service binding metadata (WSDL) stored in special
Fedora Behavior Mechanism objects.
– Fedora acts as mediator to these services.
Fedora Repository System
Client and Web Service Interactions
Service
Content
Transform
Service
Service
Fedora
Repository
System
Web Service Dispatch
Backend
Web Service
user
client
application
user
web
browser
client
application
Frontend
Content
Transform
Service
Fedora Repository
Service Interfaces
• Management Service (API-M)
– Ingest - XML-encoded object submission
– Create - interactive object creation via API requests
– Maintain - interactive object modification via API requests
– Validate – application of integrity rules to objects
– Identify - generate unique object identifiers
– Security - authentication and access control
– Preserve - automatic content versioning and audit trail
– Export - XML-encoded object formats
• Access Service (API-A and API-A-LITE)
– Search - search repository for objects
– Object Reflection - what disseminations can the object provide?
– Object Dissemination - request a view of the object’s content
• OAI-PMH Provider Service
– OAI-DC records
Fedora Repository System
Client
Application
Batch
Program
Web
Browser
HTTP SOAP
HTTP SOAP
HTTP SOAP
Manage
Access
Search
Server
Application
Web Service
Exposure
Layer
HTTP
OAI Provider
Session Management
User Authentication
Management
Subsystem
Security
Subsystem
Access
Subsystem
Object Reflection
Component Mgmt
Policy Enforcement
Object Dissemination
HTTP
Object Validation
Users/Groups
PID Generation
External
Content
Source
Policies
HTTP
Storage Subsystem
FTP
External Content
Retriever
Digital Objects
XML Files
Datastreams
HTTP
FT P
External
Content
Source
Content
Remote
Service
SOAP
Object Mgmt
Policy Mgmt
Relational DB
Local
Service
Fedora 1.2 Software Feature Set
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Open Fedora APIs
– Repository as web services (REST and SOAP bindings); WSDL interface defs
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Flexible Digital Object Model
– Content View: objects as bundle of items (content and metadata)
– Service View: objects as a set of service methods (“behaviors”)
– Extensible functionality by associating services with objects
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Repository System
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Core Services: Management, Access/Search, OAI-PMH
Storage: XML object store; relational db object cache; relational db object registry
Mediation - auto-dispatching to distributed web services for content transformation
Auto-Indexing – system metadata and DC record of each object
HTTP Basic Authentication and Access Control
Built-in disseminator services: XSLT x-form, image manipulation, xml-to-PDF
Content Versioning
– Automatic version control (saves version of content/metadata when modified)
– Enables date-time stamped API requests (see object as it looked at a point in time)
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Clients
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Fedora Administrator: GUI client to create/maintain objects
Default Web browser interface: search; access objects via default disseminator
Command line utilities (batch load, ingest, purge, others)
Migration Utility – mass export/ingest
Fedora Software Distribution Package
• Open Source (Mozilla Public License)
• 100% Java (Sun Java J2SDK1.4)
• Supporting Technologies
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Apache Tomcat 4.1 and Apache Axis (SOAP)
Xerces 2-2.0.2 for XML parsing and validation
Saxon 6.5 for XSLT transformation
Schematron 1.5 for validation
MySQL and Mckoi relational database
Oracle 9i support
• Deployment Platforms
– Windows 2000, NT, XP
– Solaris
– Linux
Future Software Releases
December 2003 – December 2004
• Fedora Object XML (FOXML)
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Internal storage format; direct expression of Fedora object model
Better support for relationships (“kinship” metadata)
Better support for audit trail (event history)
Format identifiers for dynamic service binding
• Shibboleth authentication
• Policy Enforcement
– XACML expression language
– Fedora policy enforcement module
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Web interface for easy content submission
Batch object modification utility
Administrative Reporting
Object Event History (ABC/RDF disseminations)
Better support for “collections”
New ingest and export formats (METS1.3, DIDL)
Questions?
www.fedora.info
DEMO: Basic Use Cases
Image (multiple datastreams)
Image (Mr. SID)
EAD (Rita Mae Brown papers)
Text conversion (TEI to PDF)
Basic Search