COM332 – SA3 SSADM, MERISE

SDLC SDLC has had an enormous influence in systems development Follows the structure Feasibility study Systems investigation Systems analysis Systems design Implementation Review and maintenance The term life cycle indicates the staged nature of the process By the time the review stage comes the IS may found inadequate Process start again with feasibility study

Strengths Methodologies incorporating this view have been well tried and tested The use of documentation standards ensures The specifications are completed Communicated to systems developers, users and computer operations staff People are trained to use the system Prevent missing cut over dates (to an extent) Users have opportunity to review the progress at the end of each phase Divide the system development onto phases, subdivide to more manageable tasks

Weaknesses Failure to meet the needs of the management Instability Instead of meeting corporative objectives computer are used to help low-level operational tasks Instability As business changes processes need to change to adapt to the new environment Models of processes are unstable Computer model processes have to be modified Inflexibility Systems ends (outputs) are decided in the early stages of the system development Design is output driven – designed from the outputs backwards

Weaknesses User dissatisfaction Problems with documentation Difficult to incorporate the changes once the development is underway Users asked to sign off the requirement specification in early stages of development A document prepared by the analysts, operational staff and programming staff Users first see the system on implementation and find it inappropriate Problems with documentation Documentation focused on the computer person, not on the user Lack of control Problems in estimating time, people and other resources needed due to the complexity of some phases and the inexperience of the estimators

Weaknesses Incomplete systems Application backlog Maintenance workload Exceptions are being ignored or forgotten Application backlog Users have to wait some years before the development process can get underway Development may take many months or years to complete Maintenance workload Quick and dirty solutions – high maintenance Problems with the ideal approach SDLC assumes a step-by-step, top-down approach Information systems development is an interactive process

Weaknesses Emphasis on hard thinking SDLC makes a number of assumptions There are facts that only need to be investigated and identified, there can be a best solution identified to ,solve the problem which can be easily engineered by following a step-by-step approach World of IS is concerned with people and organisation The situation encountered are problematic, ambiguous and messy Assumption of green-field development SDLC assumes all systems developed are new, there are no existing system

Major concerns in computing Meeting project deadlines System maintenance Staff recruitment and retention User dissatisfaction Changing requirements

Methodologies Process oriented Blended Object oriented Rapid development People oriented Organisational oriented Frameworks

SSADM Life cycle approach Developed by Learmonth & Burchett Management Systems (LBMS) and CCTA Used in government applications since 1981 Highly structured Has seven stages Activities and their end product of each stages are precisely defined Facilitates the use of project management method like PRINCE Cover the life sycle from feasibility to design but not implementation and maintenance

Stage 1 Investigation of current environment Stage 0 Feasibility Define scope of project Stage 1 Investigation of current environment Model existing system Stage 2 Business system options Business (logical) solutions Stage 3 Definition of requirements Transform user requirements into a specification Stage 4 Technical system options Different platforms Stage 5 Logical design Model proposed system [Stages 4 and 5 in parallel] Stage 6 Physical design Translate to physical system

Investigation of current environment Results of feasibility study are examined Scope of the project reassessed Overall plan is agreed with management

BSO (Business system option) Functionality of the new system is determined and agreed A number of business options where outlined each includes Outline of its cost  Approximate Development time scale Known technical constraints Organisation of the system (online/offline, interface to other systems, distribution) Approximate data & transaction volumes Training requirements Major benefits to the business Impact on the organisation and on other existing systems DFD and ERD are developed – specification narrative

Definition of requirements Full requirement specification and clear guidance to the design stages Centre of SSADM Investigation and analysis are replaced by specification and design DFD is used to communicate with the user User roles are defined Entity model is extended and followed by normalisation Components of each function (input, output, events or enquiry triggers) are defined Optional prototyping for better understanding of user’s requirement

TSO (technical system option) The environment in which the systems operates in terms of Hardware platforms Software (3GL, 4GL ...) Development method Technical support arrangements (in-house, outsourced, contract staff) Are determined

Logical design Physical design What the systems id required to do Dialogue structure, menu structure and design are defined for particular user roles User involvement is recommended Physical design Logical design is mapped to a particular physical environment

MERISE Widely used methodology in France The essentials of this approach lies in three cycles Decision cycle Relates to various decision mechanisms Life cycle Chronological progress of the project from start to finish Abstraction cycle Various models for processes and data Cover data and process elements with equal emphasis permits the participation of end-users, senior management and data professionals in its decision cycle

Decision Cycle Referred as approval cycle Consists of all decision mechanisms Decisions will include Technical choices regarding hardware and software Processing choices such as real-time or batch User-oriented choices relating to the user interface Identification decisions regarding the major actors of the IS and the organisation Financial decisions relating to costs and benefits Management decisions concerning the functionality of the ISs Each decision point is identified Identified who takes the decision Groups of users and system developers together discuss various options, user team produce report, discussed at the joint meeting of senior management, users and application developers. Decision is made at this point

Life cycle Strategic planning Preliminary study (domain) Maps the goals of the organisation to its information needs, and partition of organisation into domains for further analysis Preliminary study (domain) Describes the proposed information system, discuss their likely impacts, and details the associated costs and benefits Detailed study (system)  Those aspects which will be automated, including detailed specification for functional design Schedules and other documentation Development Implementation Maintenance

Abstraction cycle Key to Merise Data and processes modelled through three stages Goes from knowledge of the problem area, to making decisions relating to resources and tasks, through technical means on which to implement it Conceptual stage looks at organisation, logical stage addresses questions. Physical stage looks at resources and technical constraints.

Level Concern Data Process Conceptual What do you want to do Conceptual data model Conceptual process model Logical or Organisational Who does what, where, when, how Logical data model Logical or Organisational data model Physical or operational By what means Physical data model Operational processing model

Conceptual level establish what to do At the Logical level all the organisational alternatives are identified Identifying organisational processes, how the processes are carried out, who carries out Logical model transforms the conceptual model into a form that suitable for computerisation Deciding the database Physical level technical alternatives are identified Answer the question with what means

Merise – advantages Well tried and tested Covers strategic plan as well as life cycle from prelim study through development, implementation, maintenance, decline and replacement 3-level abstraction cycle covers data and process elements with equal emphasis Prescriptive to some extent but enables participation of end-users and senior management in decision cycle Attempts to take into account new needs and directions Many support tools available

Most important aspect of Merise Rules for creation of models Rules for converting from one stage to another Assumption that change is common so modifications will be required Support tools available