Transcript Information Systems 1

IMS5006 - Information Systems
Development Practices
Structured Systems
Analysis and Design Method
(SSADM);
Information Engineering
3.1
Structured Systems Analysis and
Design Method (SSADM)
 A comprehensive and structured approach
to systems development
 A “baseline” for comparison and
evaluation of other methodologies and for
themes in systems development
 The true successor to the traditional SDLC
approach with new techniques and tools
developed since the 1970s
3.2
Structured Systems Analysis and
Design Method (SSADM)
assumptions about information systems:
 relatively stable
 routine processing, well-defined interaction
 free-standing, developed from "scratch"
 globally defined data, processes
 complete and objectively definable
 information is well-structured
3.3
Structured Systems Analysis and
Design Method (SSADM)
assumptions about information systems development:
 essentially a linear process
 users know their current and future needs
 conceptual descriptions can be complete
 in the early lifecycle stages, system structure is more
important than system behaviour
 specification techniques should be simple and
graphical for users to understand easily
3.4
Structured Systems Analysis and
Design Method (SSADM)
assumptions about information systems, systems
development and the system developer’s roles:
 system developer is the “expert” who has the technical
knowledge to provide a solution
 system developer “owns” the methodology and
controls the development process
 users have the business knowledge and must work
with/support system developers as necessary to
ensure requirements are met
 users will own the system, must sign off
3.5
SSADM
 developed by LBMS and Central Computing and
Telecommunications Agency (CCTA) in the UK
 accepted by CCTA in January 1981 as the standard
approach within the UK civil service
requirements:
documentation
self-checking
tried and tested techniques
tailorable
teachable
3.6
SSADM
 mature, widely used in UK in particular
 typically medium to large projects
 “data-driven” due to emphasis originally on data modelling
and database technology
 later versions are more balanced:
role of users emphasised
importance of processes and functions
 version 4 in 1990
 earlier version has 6 stages (Downs, Clare and Coe 1988)
 version 4 has 7 stages (Avison and Fitzgerald 2003)
3.7
SSADM
 highly structured
 facilitates project management
 documentation “pervades” SSADM
e.g. completion of preprinted forms
 stages and their activities are precisely defined as are
their associated deliverables
3.8
SSADM
 prescriptive
 reductionist
 comprehensive
 has evolved with use: versions, CASE tool
 templates e.g. micro SSADM, maintenance
SSADM
 SDLC phases: feasibility, systems analysis,
system design
 focus on functional and technical aspects
3.9
SSADM phases
earlier version - Downs, Clare and Coe 1988: three phases
1.
feasibility study
examine the business and technical
feasibility of the project
2.
systems analysis
analyse the current system and problems,
identify new requirements and technical options
3.
systems design
logical data and process design, physical design
3.10
SSADM phases and stages
1. feasibility study
stage 01: problem definition
stage 02: project identification
2. systems analysis
stage 1: analysis of systems operations & current problems
stage 2: specification of requirements
stage 3: selection of technical options
3. systems design
stage 4: data design
stage 5: process design
3.11
stage 6: physical design
(Downs et al 1988)
SSADM
characteristics

Downs, Clare and Coe 1998
hierarchical structure:
phases, stages, steps, tasks, techniques

data driven design

cross-checking

separation of logical and physical

tailorable

user communication

quality assurance

documentation standards
3.12
SSADM techniques
Downs, Clare and Coe 1988

data flow diagrams

logical data structuring (LDST)

entity life histories

dialogue design

relational data analysis (RDA)

composite logical data design (CLDD)

process outlines

system flow charts
3.13
SSADM: other SDLC phases
 construction and implementation:
output of physical design can interface with
1.
traditional programming (JSP)
2.
application generators
3.
application packages
 prototyping can be used in design and construction
 automated support tools are available
 a project management methodology can be used
 organisational IT/ IS planning:
use a planning methodology
e.g. LEAP developed by LBMS
3.14
SSADM: later versions
 version 4 - Avison and Fitzgerald 2003: five phases, seven stages
feasibility study
0
Feasibility
requirements analysis
1
Investigation of current environment
2
Business system options
requirements specification
3
Definition of requirements
logical system specification
4
Technical system options
5
Logical design
physical design
6
Physical design
3.15
SSADM version 4:
Feasibility Study
 ensure the project identified in planning phase is feasible
(= technically possible) and benefits > costs
 prepare for the study (assess the scope)
 define the problem (compare requirements with current
situation)
 identify and select feasibility option (consider broad
alternatives in terms of business requirements and
technical options)
 produce feasibility report
 techniques: interviewing, document review etc., broad
DFDs and ER model
3.16
SSADM version 4:
Requirements Analysis
1 Investigation of current environment

detailed physical DFDs and ER model of current
processing and data,

logical DFDs, functional and non-functional
“requirements catalogue”,

scope and feasibility study results re-examined
2 Business system options

cost-justified requirements only, determine and agree on
functionality,

business options meeting minimum requirements: cost,
technical constraints, development schedule, benefits
and impact, training, etc.
3.17
SSADM version 4:
Requirements Specification
3 Definition of requirements
 logical data model (ER) extended,
 attribute collection and normalisation,
 DFDs extended,
 full documentation of all data, processes and
events,
 entity life history diagrams,
 prototyping can be used for important dialogues
and menu structures
3.18
SSADM version 4:
Logical System Specification
 These stages occur in parallel:
4 Technical system options
 environment in which system will operate - hardware,
software, contraints (e.g. performance, security, service
levels)
5 Logical design
 design what the system is required to do
 user involvement, refer to any prototypes, define
dialogues and menu structures for specific user roles,
ELHs used to define update and enquiry processing,
data validation rules etc.
3.19
SSADM version 4:
Physical Design
map the logical design onto a specific physical environment:
functional component implementation map (FCIM)
6
Physical design
 roles of the technologists stressed
 users and analysts verify final design satisfies user
requirements,
 convert data model, specify programs, procedures etc.
 specific activities depend on specific environment (system
type, size, technical platform etc.
SSADM ends: subsequent activities build, test and install the
system
3.20
SSADM
 a structured approach: well-defined structure for
its use, for training, and for managing projects
 supported by CASE tools
 clearly defined deliverables and quality review
checkpoints
 relies on availability of skilled personnel
 systems development is about providing
technical solutions to business problems
3.21
Information Engineering
 Martin and Finkelstein (1981), Martin (1989), several
versions
 data oriented methodology
 full lifecycle coverage
 organisation-wide perspective on planning of information
technology and information systems
 top-down analysis and development of organisation’s
applications
 focus on data and activities
 well-supported by CASE tools e.g. IEW, IEF
 has evolved
 widely used
3.22
Information Engineering
evolution
 data base technology
 data analysis and data management
 strategic data models, procedure formation
 4GLs and “productivity tools”, e.g. code generators
 alignment of information systems planning with strategic
business planning
 process modelling techniques
 CASE technology, “encyclopedia”, knowledge
coordinator
 RAD (Rapid Application Development)
 object-oriented concepts
3.23
Information Engineering
 data centred:
model data requirements first, processes later
(data is more stable)
applications will be integrated by a common data
framework
 information engineering:
“an interlocking set of formal techniques in which
enterprise models, data models and process models are
built... and are used to create and maintain data
processing systems”
James Martin (1986)
 use of diagrams as a communication and representation
3.24
tool
Major phases of Information
Engineering
 information strategy planning
to build an information and technology architecture to
support business strategy and objectives
 business area analysis
to identify data and function requirements of each
business area
 individual systems planning
 systems design
to complete logical specifications for a system and
convert these into physical design specifications
 construction
to generate code, test, and install the system
 cutover
3.25
Phase 1 - information strategy
planning:
 corporate management and planners assess the
organisation:
business mission, objectives, CSFs, performance
measurements, organisation structure, current situation




construct corporate data model
determine major business functions
identify business areas, including goals and CSFs
determine:
information architecture (global entities and business areas)
information systems architecture (business sytems)
technical architecture (technology: hw/sw/comms)
information strategy plan (priorities)
3.26
Phase 2 - business area analysis:
 identify and model in detail the fundamental data and
activities required to support a business area
 ensure that requirements are independent of technology
 ensure that requirements are independent of current
systems and procedures
 ensure that requirements enable business area’s goals
and CSFs to be supported
 ensure that requirements are independent of the current
organisational structure
 a high-level executive sponsor is necessary
3.27
Business area analysis: steps
 extract the relevant entity relationship model and businessfunction decomposition models
 identify relevant departments, locations, business goals, CSFs
 create a preliminary data model: identify events, entity life
cycles, initial attributes
 create a preliminary process model: decompose the functions
into processes
 model data and processes of existing systems for comparison
 involve all affected end-users in iteratively building:
a detailed data model, a detailed process model, entity /
process matrices
3.28
 identify and prioritise system development projects
Business area analysis:
techniques
 data model
entity relationship modelling
attribute collection
normalisation
canonical synthesis
 process model
process decomposition models
process dependency diagrams
 data and activity interaction
entity lifecycles
process / entity matrix
3.29
Information engineering:
phases 3 and 4
 Phase 3 - individual systems planning
use JRP for individual systems planning
 Phase 4 - system design:
concerned with how selected processes in the business
are implemented in procedures and how these
procedures work
use the logical data and process models to design the
external representations of the system
direct end-user involvement is essential
identify reusable procedures
use prototyping
use JAD
3.30
System design techniques
 prototyping
 detailed process models: procedure design using
access path and volumes analysis, dialogue flows
and menu structures,
 physical database design, file design,
 screen displays
 menu flows
 report layouts
 on-line procedures and software
 batch procedures and software
 design verification and testing
3.31
Information engineering:
phases 5 and 6
 Phase 5 - construction:
technical design, create physical databases
create modules and programs, unit testing
system testing, documentation
 Phase 6 - cutover:
conversion
final testing
conduct training
install the system, review implementation
3.32
Information Engineering
features:
 organisation-wide perspective aligned with strategic
business planning
 comprehensive
 emphasis on user involvement e.g. JAD, JRP
 evolves by incorporating new techniques, concepts,
technologies e.g. RAD, object-oriented concepts
 evolves from practice e.g. shortened ISP phase
 emphasis on automation e.g. 4GLs, I-CASE, prototypes
 primarily for database transaction processing systems
 little event or behaviour modelling
3.33
Information Engineering
features:

after ISP phase, activities can proceed in parallel

high level data and process model (co-ordinating
model) enables this by highlighting interfaces and
dependencies between systems etc.

flexible paths through the methodology
e.g. reverse engineering and re-engineering
3.34
References
 Prescribed text:
Avison, D.E. & Fitzgerald, G. (2003).
Information Systems Development:
Methodologies, Techniques and Tools. (3rd ed),
McGraw-Hill, London.
Chapters 20.1, 20.3
3.35