1. CS 501: Software Engineering Fall 1999
Lecture 3
Requirements Definition

2. Administration
Web site: Additional project descriptions, recitation sessions.
Project team formation: Newsgroup, Monday recitation session.
Project: What is a client?
Tools for managing large programs.

3. Requirements Definition and Analysis
System and
Software design
Implementation
and Unit Testing
Integration and
System Testing
Operation and
Maintenance

4. Example: Library of Congress (A Partial Failure)
Outline Description
The Library of Congress requires a repository system to store and make accessible very large amounts of highly varied material over long periods of time.

5. Chronology 1993-94 CNRI carries out research on architectures for
digital libraries
CNRI implements prototype repository for
Library of Congress
CNRI and Library of Congress carry out requirements
definition

6. The Repository
Repository
Users
Handle System
Search System

7. The Repository Network Based Storage and Access to Digital Objects
All information stored as typed data in digital objects.
A single digital object has both data and meta-data.
Identification of digital objects is by location independent, persistent URNs.
Access management built into methods for accessing digital objects.

8. Repository Access Protocol (RAP)
RAP: 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
A CORBA-based repository
RAP is a set of classes defined by a CORBA IDL
Protocol is Internet Inter-Object Protocol (IIOP)

9. Access Management Digital material Attributes User Policies Operations
Roles

10. Structural Metadata for Complex Objects
Several representations:
thumbnail image
reference image
archival image
Metadata
Each representation may have its own metadata

11. Structural Type: pix1 Identifier Data thumbnail gif reference jpg
loc.ndlp/amrlp
Data
thumbnail
gif
reference
jpg
archive
jpg
pix1
Metadata
object-md

12. Repository: Research Achievements
1. CORBA implementation of repository access protocol.
2. Integration of persistent naming through handle system.
3. Use of structural metadata to describe complex objects, elementary typology.
4. Access management framework and implementation.
5. Applet-based middleware for user interfaces.
6. Information visualization program to view the structure of large collections.

13. Good Discoveries During Prototype
 Structuring complex information in digital libraries
 Data driven digital library interfaces
 Comparison of object-oriented, relational, and file
based storage systems
 Naming and identification of library objects
 Boundaries of required repository system

14. Bad Discoveries During Prototype
 Resistance to change within Library of Congress
 Technical weakness of Library of Congress
 Gaps in CNRI architecture

15. Mistakes  Confusion of objectives (research and implementation)
 Failure to involve all stakeholders
 Over ambitious (no proper feasibility study)

16. The Requirements Process
Feasibility
Study
Requirements
Analysis
Requirements
Definition
Requirements
Specification
Feasibility
Report
System
Models
Definition of
Requirements
Requirements
Document
Specification of
Requirements

17. Requirements Definition
High-level abstract description of requirements:
 Specifies external system behavior
 Comprehensible by customer, management and users
Should reflect accurately what the customer wants:
 Services that the system will provide
 Constraints under which it will operate

18. Library of Congress Requirements Study
Team (all experienced): Librarian, Software Engineer (CNRI),
Computing Project Leader (Library of Congress), + 2 others
Advisors: Mailing list of about 20 knowledgeable stakeholders.
Timetable: Preliminary report (2 months). Final report (1 month).

19. Functional Requirements
 Support for complex digital objects
 Access management
 Identification
 Information hiding
 Open protocols and formats

20. Object Administration System
DRAFT OVERVIEW OF ITS SUPPORT
FOR NDLP PRODUCTION AND DELIVERY OF AMERICAN MEMORY
NDLP collections
already released
Coolidge collection
(for repository test)
NDLP collections
in conversion
Future
NDLP collections
Other applications
and materials
NDLP Workflow
Tracking Support
Current Storage Structure
(in Unix files, by aggregate)
Object Administration System
ILS
Repository
Index Generation
(including pre-processing)
American Memory User Interface
(retrieval, navigation, & display)
AM user interface plus
access management
for objects/collections
Other User Interfaces
(e.g. RLG, OCLC, DLF partners)
ILS OPAC Interface
Supporting infrastructure
Handle assignment
& registration
Handle resolution
Handle-server
NOW
FUTURE

21. Non-functional Requirements
Environment:
 Estimates of sizes, numbers of users, etc.
 Reliability and performance measures and targets
Preferred:
 Hardware and software systems (IBM/Unix)
 Database systems (Oracle)
 Programming languages (C and C++)

22. Evolution of Requirements
 If the requirements definition is wrong, the system will be
a failure.
 With complex systems, understanding of requirements
always continues to improve.
Therefore...
 The requirements definition must evolve.
 Its documentation must be kept current (but clearly
identify versions).

23. Reading Before next class, read and be ready to discuss:
Sommerville: Chapters 4, 5, 6 and 7, pages 63 to 136.