Software Engineering System analysis and Design

Steps in System Analysis and Design I dentification of the problem F easibility Study System A nalysis System D esign System D evelopment T esting & Debugging System I mplementation System M aintenance

Identification of the Problem Computable solution

Feasibility Study Economic feasibility Technical feasibility Cost-Benefit analysis –Financial benefit –Quality improvement –Efficient –Easy

System Analysis System Analyst Study the current system –Identification of entities & functions (nouns & verbs) –Entity relationship –Study of the data flow through the system between subsystem (sub processes) Input, output and storage –Process description (input, actions on data, output and storage of data/information) –Methods of obtaining details – Interviews. Questionnaires, observations, documents

System Analysis contd… Specifications of the new system

System Design Preliminary Design –Screen layouts (data input), report formats, in paper and ink –Entity relationships, database structures, data security, –Prototype – client- to complete analysis Throw-away prototype Evolutionary prototype Detailed Design

A prototype is an early version of the system that exhibits the essential features of the later operational system. Some … prototypes may evolve into the actual production systems whereas others are used only for experimentation and may eventually be replaced by the production system. Prototype

Detailed Design User interaction –Login screens –Data input screens –Report formats (by request or automated) –Security –Search facilities Database structure Process descriptions Data dictionaries

Detailed Design contd… Software specifications –Operating system –Utilities –Antivirus Hardware specifications –Servers and workstations –Network cabling (Local and internet) –Printers, barcode readers…. –UPS

CASE Tools Computer Assisted Software Engineering –Computer software is used to design the system –System specifications are input to the software –Design document is automatically created –Finally the database and the computer program is automatically generated in a language decided by the developer.

System Development Conversion of the design into computer programs –Modular approach: Each module is developed by individual programmers –Finally modules are integrated into one system

Advantages of modular approach Easy to manage – distribution of workload Parallel development - save time Easy to test and debug Easy to trouble shoot and maintain Use of individual expertise Reuse of software modules

Testing & Debugging (at the developer’s lab) Each module is separately tested and debugged Then modules are combined and tested & debugged Then whole system is built, tested & debugged Test data: –Normal, Abnormal, Extreme data are used

Testing & Debugging (at the client’s site) System accepting test – with the client Problems due to –Bad or wrong hardware –Bad or wrong OS –Cabling problems –Environmental problems: network cables near tube lights or any other interference

Implementation Installation of hardware and relevant software Creation of databases and initialization Installation of front-ends (user interfaces) at individual machines Training of operators and officers Provision of user manuals –Installation instructions –Simple troubleshooting procedures

Implementation methods Direct implementation Phase by phase implementation Parallel implementation

System Maintenance The developers will monitor the system for a short period Attend to minor changes and repairs

System Life Cycle (SADLC) Analysis Design Development Implement ation Maintenan ce

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

Systems Development Life Cycle (SDLC) Feasibility Study Requirements Analysis Requirements Specification Logical System Specification Physical Design S S A D M Strategy Planning Implementation Maintenance Feasibility Analysis Design

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 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 Structured Systems Analysis and Design Method (SSADM)

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

SSADM: later versions version 4 - Avison and Fitzgerald 2003: five phases, seven stages feasibility study 0Feasibility requirements analysis 1Investigation of current environment 2Business system options requirements specification 3Definition of requirements logical system specification 4Technical system options 5Logical design physical design 6Physical design

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

SSADM version 4: Requirements Analysis 1Investigation 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 2Business 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.

SSADM version 4: Requirements Specification 3Definition 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

SSADM version 4: Logical System Specification These stages occur in parallel: 4Technical system options environment in which system will operate - hardware, software, contraints (e.g. performance, security, service levels) 5Logical 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.

SSADM version 4: Physical Design map the logical design onto a specific physical environment: functional component implementation map (FCIM) 6Physical 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

Waterfall Model e.g., Structured Systems And Design Method (SSADM)

Waterfall Model of SADLC

Process Descriptions Process ID: P001 Process Title: Calculate Average Input: Marks of Math and Science from Marks table Output: Average Marks Process Logic: Begin Get Math marks Get Science marks Add together and place in Total Divide Total by two and place in Average Output Average End