System Analysis And Design

Module System analysis and design

1. The objective of module:

Provide: System Visions of Managers, Users, Technicians Basic knowledge of systems’ life cycle System analysis and design techniques Some analysis and design skills and experiences

2. Module “Requirements to learners”

Basic knowledge of system and Information technology Ability to understand and executive the supporting tool of analysis and design Interest in analysis and design fields

3. System development Life-cycle The principal phases in the system development: •Investigation •Analysis •Design •Implementation Recommended percentage distribution: •Investigation, Analysis, Design: 50%-60% •Implementation: 40%-50%

4. Main contents of module: Chapter 1: Introduction to Systems 1.1. Overview 1.2. System approach 1.3. Example Chapter 2: Systems Analysis 2.1. Analysis of Structured System 2.2. Information analysis, data model 2.3. Strengthening of Information structure – Relationship model 2.4. Completion of Information analysis 2.5. Summary of analysis process

4. (continue) Chapter 3: System Design 3.1 The overall designing specifications 3.2 Structured design as process 3.3 User- Computer interface design 3.4 System monitoring design 3.5 Organizing the system’s components 3.6 Analysis of data usage and logical navigation 3.7 Design of databases 3.8 Example References Index

1.1. OVERVIEW

Definition of System Participants to system development System development life – cycle

Participants to system development •User •Management •Auditors, quality assurance people, and ‘standards bearers” •Systems analysts •Systems designers •Programmers •Operations personnel

System development life – cycle •Initial investigation •Feasibility study •General design •Detailed design •Implementation •System audit

1.2 System approach

System approach The system's requirements Users requirements Technical requirements Some principals Investigation methods Survey report

System approach The WaterFall Model •Systems analysis; •Systems design; •Systems build and test; •Systems introduction and transition; •Maintenance of production status systems. The Spiral Model •Incremental approach to systems development •System divided into smaller sub-sets for development and delivery. •End-users’ functionality provided at regular intervals, rather than at the end of a waterfall development.

The system's requirements Suitable with the general strategies Supporting decision maker Competition edge Return on Investment Supporting operational management Improving information communication Impacts of information products Ability to implement more quickly and better.

Users requirements Easy access; System must be: • Solid and stable; • Accurate information; • Easy to maintain and restructure; • Quick in identifying and correcting mistakes; Interface: • Suitable with users’ working style of users; • Stable; • Easy to control data; • Independent and flexible.

Technical requirements Information technology equipment must be suitable with the volume of information that is to be processed; Everyday information requires special care; Accuracy of information is important; New system is required to resolve issues that current system fails to process due to information complexity Popular issues:

Some principals Investigation methods 1. Survey methods: Interview 2. Observation methods: •Official observation •Unofficial observation 3. Questionnaire method: (complicated and ineffective for inexperienced analyzers) •Objectives and main contents •Categories of data that will be used •Data contents in each category.

Survey report Main items: •Objectives of the system; •Inter-connection between related departments; •Details of the current system; •Future system and sketchy estimate of costs and benefits; •Advice; •Time frame and plan for system development; •General description (non-technical); •Original document; •Evaluation of current system in: organizational structure, technology, information system, users’ IT skills, policy renovation...

Example Library management system of Institute of Information Technology (IOIT) Survey main contents •Relations between the current library management system and other library management systems; •Main jobs of the library management system; •Necessary improvements expected in the new computer system. Interview questions: •What are the main jobs of the library management system? •What is the function of each job? •How are the jobs currently done? •Who is responsible for them? •What are the restraints and difficulties in each job? •Whom does the library serve? and so on

2.1 Analysis of Structured System System analysis Nature of analysis Importance of analysis in system’s life cycle Roles and requirement of system analysts Analysis supporting tools Functional diagram (FD) Data flow diagram: describe the information flow in the system Main components of data flow diagram

2.1. (Continue)

Data dictionary Process specification Data flow diagrams in the example of library management system Entity relationship diagram (ERD) Entity relationship diagrams in the example of library management system

System analysis Structural system analysis’ main characteristics: Developed in “top – down” order; Analyze the current system and new requirements of users; Define a format for the future system; Major tools used in structural system analysis: •function diagram •data flow diagram •data dictionary •process specification •entity relationship diagram;

System Analysis (Continue)

•Acknowledge users’ role in different steps of system development; •Supported by advanced technology in both hardware and software, this method is less complicated •Structural analysis together with prototype method give ideas of the new system and help make best use of both methods.

Nature of analysis Main steps of system analysis process Identify the operation of the existing system; Understand what the existing system is doing; Understand the need of the users; Decide on what the new system should be doing; Decide on how the new system will function. Tool for analysis;

Importance of analysis in system’s life cycle Main phases: •Survey •Analysis •Design •Implementation •System testing and approving •Installation and maintenance. Main subjects of system users, mangers and technical experts (including analysis, design and program specialist...)

Roles and requirements of systems analyst

System analysts’ roles System analysts’ required qualifications

System analysts’ roles

Archaeologist and scribe Innovator Mediator Project leader

System analysts’ required qualifications More than just the ability to draw flowchart and other technical diagrams; Skills to interview users, mediate disagreements; Application knowledge to understand and appreciate the user’s business; Computer skills to understand the potential uses of computer hardware and software in the user’s business; Able to view a system from many different perspectives; Able to partition it into levels of subsystems; Able to think of a system in abstract terms as well as physical terms.

Analysis supporting tools Functioning diagram Data flow diagram Relationship diagram... Analysts using models to: Concentrate on important features of the system, pay less attention to less important ones; Able to respond to changes or changes in user’s requirements with low cost and risk; Properly understand users’ environment and write documents in the same way that designers and programmers construct the system.

Functional diagram (FD) •Functional diagram is a process of division, from a higher function to appropriate smaller functions. •Diagrams need to be presented clearly, simply, exactly, fully and balancely. •Functions of the same level has the same level of difficulty need to be on the same page. •The function hierarchy diagram in the current example

Example (FD) Library Management System

Readers Management

Doc uments Management

New reader receiving

Documents Classifying

Dept_no Checking

New books Inserting

New department register Reader_no allocating

New magazines inserting

Doc uments Lookin g up Books looking up Magazines looking up

B/R ticket Management

System Reports

B/R ticket Receiving

Document Report

Checking

Department Report

Replying

Function Hierarchy Diagram

Overdue Readers

Data flow diagram: describe the information flow in the system Data flow diagram supports 4 main activities: •Analysis: DFD used to determine requirements of users •Design: DFD used to map out plan and illustrate solutions to analysts and users while designing a new system •Communication: DFD is simple and easy to understand to analysts and users; •Documents: DFD used to provide special description of requirements and system design.

DFD (Continue)

Data flow diagram can be described in the following ways: •What functions should the system perform? •Interaction between functions? •What does the system have to transfer? •What inputs are transferred to what outputs? •What type of work does the system do? •Where does the system get information from to work? •And where does it give work results to?

Main components of data flow diagram • Process • Flow • Storage • External factors • Internal factors. You can construct DFD of system with the following guidelines: • Choose meaningful names for processes, flows, stores, and terminators • Number of processes • Re-draw the DFD many times • Avoid overly complex DFD • Make sure the DFD is consistent internally and with any associated DFD

Data dictionary Data dictionary defines the data elements by doing the followings: • Describing the meaning of the flows and stores shown in the data flow diagrams; • Describing the composition of aggregate packets of data moving along the flow; • Describing the composition of packets of data in stores; • Specifying the relevant values and units of elementary chunks of information in the data flows and data stores. • Describing the details of relationships between stores that are highlighted in an entityrelationship diagram.

Process specification Tools used in process specification: •Decision tables •Structured English •Pre/post conditions •Flowcharts, and so on. •Process specification expressed in a form that can be verified by the user and the systems analysts; Process specification expressed in a form that can be effectively communicated to the various audiences involved.

Data flow diagrams in the example of library management system 1 Manage Readers

Readers register

Readers

Reply (with reader_ no)

4 Process Borrowing/ Returning ticket

Check readers

Supply documents

Dept /Readers

Check documents

Look up

B/R ticket

2 Manage documents Report Leader of Institute

Return doc_no

3 Look up documents

Documents

B/R ticket

Documents suppliers

Look up documents

Check & update

Le nd Or G iv e B ack d oc ume nt s

R ep ly To R ead er

Readers

5 Report about Library System Report Departments in Institute

Data flowdiagramhigh level

Borrow excess time limit Readers

Entity relationship diagram (ERD) Main components: Entity Attribute Relationship One - one relationship One - many relationship Many - many relationship

Entity relationship diagrams in the example of library management system BOOKS COL LECTIONS #COLL _NO * COLL _NAM E

SPECIALITY #SPE C_ NO * SPE C_ NAME

DEPARTMENTS #DEPT_ NO * DEPT_ NAME

#BOOK_ NO * BOOK_ NAME * SIZE * TI ME_ PUBL * Y E AR_ PUBL * PUB_ HOUSE o COST * AUTHOR o CHIEF_AUTH o COMP_AUTH o REV_ AUTH * LA NG_ NO * NATI ON_NO * SPE C_ NO * COLL _NO o KW_MASTER o KW_SLAVE o COMMENT

LANGUAGES #LA NG_NO * LA NG_NAME * LA NG_VN * LA NG_SY S

NATIONS #NATI ON_NO * NATI ON_NAME * NATI ON_VN

READERS #READER_ NO * READER_ NAME * DEPT_ NO o ADDRESS o BI RT H_DATE o COMMENT

B/R BOOK_TICKETS #READER_NO #BOOK_ NO #BORROW_DATE o RETURN_DAT E o COMMENT

Entityrelationship diagram (Books)

Comment: #: Primary key *: Not null o: Option

2.2. Information analysis, data model

 Data model  The advanced data modeling

Data model Two steps to develop a data model: • Defining entity types • Defining relationships • 1st approach: using 3 types of information to decide which entities need storing details about •Information relating to one of the objects of the system; •Information relating to the major assets or resources used in the system; •Information about planning and controlling. •2nd approach (most popular) Based on the surveys on the current system and projections of the future system, analysts choose the right words to describe the system’s operation (its functioning)

The advanced data modeling

Some contexts where modeling techniques are not enough to display in models and yet more techniques are required: • Optional relationship • Abstract data type • Recursive relationships

2.3 Strengthening of Information structure – Relationship model Strengthening of information structure relationship model Identifying attributes Normalization EXAMPLE - Normalization process Defining relationships and Models comparison

Strengthening of information structure relationship model Main steps of creating a relationship model and using it to test data model: .Define necessary attributes in the to-be-built system; .Define type of entity suitable to attributes to limit copying and data redundancy (normalization technique); .Define potential relationships within the lists of established attributes for every entity by choosing linking attributes. .With known attributes, types of entity and relationship, it is possible to construct a scheme similar to intuition data model. .Estimate quantity of entity for every table via relationship normalization

Identifying attributes Basis to identify entity attributes’ details: Interviewing users; Examining report forms and other documents Estimation or intuitional identification of attributes is formed. Analysts’ experience and knowledge in the field under question

Normalization A process of surveying lists of attributes and applying a range of analysis principles to the lists in order to make them meet the followings: •Minimization of repetition; •Avoidance of redundancy; •Elimination of ambiguity. Three essential normalizations •First normal form (1NF) •Second normal form (2NF) •Third normal form (3NF)

Normalization (continue) Analyst must double check the following points: •Is each entity in 0NF, 1NF, 2NF or 3NF? •Check optionality of relationships •Make sure that no two entities have the same unique identifier •Remove “attributes” which are really M to 1 relationships.

Normalization (continue) * In short, to normalize, analysts must finish the following steps: •Create a list of data items •Identify derived items •Choose a unique identifier (a “key”) •Remove repeating groups for that key (and copy across original key) •Remove “part - key” dependencies (and copy across that part of the original key) •Remove non-key dependencies •Bring together data items with the same key.

Defining relationships Tools : Entity / Key matrix....... Models comparison Between • Outline of the intuitive data model • Relationship model

2.4. Completion of information analysis

Completion of information analysis EXAMPLE: Outcomes of professional rule analysis

Completion of information analysis

Main contents: •Corporation of new requirements •Supporting tools and materials •Summary of analysis process

EXAMPLE: Outcomes of professional rule analysis .The library manages two main kinds of document - books and magazines. .All information about books is stored in a book table which includes a list of attributes. .All information about magazine is stored in a magazine table which includes a list of attributes: .A new documents will be registered in the finding fields (for readers to look up) in the library card. .Library manages other activities

Summary of analysis process Main contents of summary: •Contents and scale of system analysis •Summary of management work •Function diagram •Data flow diagram •Data model •Relationship model •Process description •Data dictionary Result of this phase is the 3 important diagrams used in System Design •Function Hierarchy Diagram •Data Flow Diagram •Entity Relationship Diagram.

3.1 The overall designing specifications  Definition of structured design  Relationship between system analysis and design  Some guidelines on selection of design methodology  Tools and Techniques of design  Example

Definition of structured design Several definitions Guidelines to maximize the benefit of introducing Structured Design into an organization: Make it clear from the start that Structured Design is not a remedy for any problems of the organization Obtain support from anyone who may be affected by this change Emphasize the flexibility that Structured Design provides and downplay the misconception that it is restrictive

Relationship between system analysis and design

Demonstrated in models used in both Analysis and Design phases

Some guidelines on selection of design methodology Necessary considerations when selecting a tool: Will it help the team arrive at an understanding of the system underdevelopment; Is it easy to learn? Easy to use? Will it serve user-analyst communication? What does it cost? What data structures does it use? What data flow and control features does it have? Is the technique manageable?

Tools and Techniques of design Major selected tools: Information System Design and Optimization System (ISDOS) Pseudo-code Structured design (SD) Jackson Design methodology (JDM) Hierarchy Plus Input, Process, and Output (HIPO) Structured Analysis and Design Technique (SADT) Entity Relationship Model (E-R Model) Data Structure Diagram (DSD) Semantic Data Model (SDM) CASE*Method

Example

Inputs of system design phase (outputs of system analysis phase): -Function Hierarchy Diagram -Data Flow Diagram -Entity Relationship Diagram

Example (Continue) Main tasks in system design: 1. Define which functions have to be done by human, and which functions have to be carried out by computer, so we have DFD system (half-physical) 2. Design database 3. Design the human/computer interface With the library management system, the system design phase concentrates on the following main parts: -determines the computer system -designs modules -designs database

3.2 Structured design as process

The phases of Structured Design Logical Design Phase Physical Design Phase Identification of the computer system

The phases of Structured Design

Logical Design development Physical Design development

Logical Design Phase The activities occuring during the Logical design phase: Develop preliminary design Define the man-machine and machinemachine boundaries on DFD Transform E-R-A Model into Relational Model Normalize Relational Model Prepare Database access Model Verify against Normalized Relational Model Transform leveled DFDs into first-cut structure chart

Logical Design Phase (c) Refine structure Chart using coupling, cohesion and adding additional functions, as necessary. Develop pseudo-code(structured English) Revise Event Mode Revise Relational Model Update Lifecycle Dictionary Perform consistency check among Structure Charts, pseudo-code, Event Model, E-R diagrams, Relational Model. Ensure that all parts of the design are accurate and mutually supportive.

Physical Design Phase Develop Detailed Design Review Preliminary Design Package Develop final Structure Chart Update Lifecycle Dictionary to reflect physical characteristics Revise pseudo-code Perform coupling and cohesion analysis Revise Event Model Reconcile all elements of module design package Map to DBMS Data Model

Identification of the computer system

Define borderline between computers and users Determines the computer system in presented example

example 1.2 Check Dept_no 1.1 Receive New reader

L ook up

Dept/Readers

register

Readers

A llocate new dept (if not have dept)

Readers A llocate new reader_no (if had dept)

A llocate new reader_no

1.3 Register new department User

Computer

New reader_no

update

Data flow diagram (Function 1).

1.4 Allocate Reader_no

update

Dept/Readers

3.3 User – computer interface design

User - Computer interface design Example

User - Computer interface design Dialogue design Significant criteria for the evaluation of dialogue type: Easy to use Easy to learn Processing and responding speed Easy to develop Significant types of user-computer interface design

User - Computer interface design (c)

Display design Three main types of display: -Menu display -Dialogue display -Data entry display

User - Computer interface design (cc) Outputs Design Basic design principles of outputs design: Notes, headings, and output formats should be standardized whenever possible. The arrangement of information should be logical. Acronyms and abbreviations in output should be avoided especially when the output will serve novice users. Algorithms and assumptions on which calculations are based should be available to users of the output. The user should be able to locate needed data quickly without having to search through all of the data.

Example Screen design: General requirement of modules: Modules must have a common toolbar, including the following buttons: Design the looking up document function Design output The output of the library management system is three main reports Report about document Report about lending and giving back documents of departments Report about overdue readers: listing all readers who are overdue now.

3.4 System monitoring design

 System monitoring design  Method of analyzing controls

System monitoring design Significant aspects should be protected by control: Accuracy Safety Privacy The most popular method of analyzing controls is based on the data flow diagram (DFD).

Method of analyzing controls

 Define the threat of the system.  Design necessary controls.

3.5. Organizing the system’s components

Organize the program in sub-systems. Grouping criteria Designing approach Tools and modelization techniques

Grouping criteria Entity group Events group Accuracy group Three general situations where the grouping of modules and programs are possible: Modules on batch and online appear in the same area, or have the same relationship with a type of data Users in different responsibility levels working on the same data Each user has different responsibilities relating

Designing approach

Two modules types: • functional module • intersection module

Tools and modelization techniques The two models popularly used in this phase. These 2 diagrams must be fully consistent and this one is used to test, modify and improve the other. System diagram based on computer Computer data flow diagram. Difference between computer DFD and system DFD: the non-computer process is presented in system DFD become “internal factor” of new model. The main components of the diagram: Internal and External factor on top of the diagram Intersection modules Functional modules Relating files

3.6. Analysis of data usage and logical navigation

 Analysis of data usage and logical navigation  Path analysis diagram  Navigation model

Analysis of data usage and logical navigation

The three main tools: Path analysis diagram Navigation model Data usage schema

Path analysis diagram Main purposes of path analysis diagram: To check whether the necessary information for the process can be achieved by using data model To describe the complication of the process and the data model already built, whereby assisting physical database designer to optimize his data structure.

Navigation model Navigation model will give an overview of data usage throughout the system; it gathers information of individual access paths in different processes and links them to the data model already built in the analysis phase. Navigation model is a data model of the system with individual access paths added. Navigation model is used in necessary cases. Data usage schema This chart contains: Details of each entity type that get accessed in the model Number of entities that may be accessed to Frequency, features used for access Other aspects assisting designers to build up the database.

3.7 Design of database  Design of Databases  Physical database design  Most of a First – cut Data Design  Physical storage structure design  Privacy  Integrity sub-system designing  Database design in presented example

Design of Databases Main components of a database: Conceptual schema Database schema Physical schema Physical storage structure Back-up and Recovery System User interface Mapping module from logical to physical Privacy sub-systems Integrity sub-system

Physical database design Objective of this phase is to give the system definitions of data and to build data structure (file/table) ready for installation base on the following information: Constraints of user’s system implementation Details of data usage analysis: data model, relationship model, path analysis diagram, navigation model and data usage chart.

a First – cut Data Design Some basic mappings: Entities become tables Attributes become columns Unique identifiers become primary and unique key constraints. Relationships become foreign key columns and constraints. Note: Producing the first – cut is only the first stage in building a complete data design.

Physical storage structure design Important aspects in designing the physical storage structure: Data independence  All relationships between entities described in conceptual schema are demonstrated by effective accessing paths in the physical storage structure  All accessing requirements by application programs sent to physical schema are presented by a logical language independent with the data structure being used, including physical storage structure. Advantages of an independent data database: New application programs can be added to the system at minimum costs. The installation environment can be changed more easily

Privacy Main functions of private module: Identify users List components of database schema corresponding to the components of database that users wish to have access to Check accessing ties to see whether an access is legal - Ids, passwords or magnetic cards The most popular kinds of constraints: Privacy constraints depicted as users’ accessing authority exclusively to the parts of physical storage structure, such as limiting access to records of data table Some constraints limit the access to several functions of the program or relevant data files. Other constraints may require special procedure and are often located at in/out application program.

Integrity sub-system designing Integrity sub-system is responsible for maintaining the integrity by protecting database against illegal changes and damages in the whole system, which may cause data errors. Data errors can be seen in the following cases: Data are not updated frequently. Data are updated simultaneously Data are damaged while being coded, changed or transmitted from a distance Data are damaged while being stored due to hardware faults.

Integrity sub-system designing (c)

One of the most important aspect to secure the database against errors is to back-up the data regularly and recover the data when necessary Lock strategy Data back up Recovery

Database design in presented example Base on the entity diagrams in the system analysis phase, we continually design the tables correspondent with them as the following rules: Entity

becomes

Table

Attribute

becomes

Column (field)

unique identifier becomes

primary key