Unit 2: Systems Analysis and Requirements

SYSTEMS ANALYSIS AND REQUIREMENTS

Learning Outcomes:

1.User and/or market requirements

i.Requirements Determination

ii.What Is a Requirement?

iii.The Process of Determining Requirements

iv.The Requirements Definition Statement

2.Project specifications

3. Structured analysis

4. Decision tables or trees electrical interface

 

Requirements Determination

Requirements determination is performed to transform the system request’s high-level statement of business requirements into a more detailed, precise list of what the new system must do to provide the needed value to the business.

During a systems development project, requirements will be created that describe what the business needs (business requirements); what the users need to do (user requirements); what the software should do ( functional requirements); characteristics the system should have (nonfunctional requirements); and how the system should be built (system requirements).

During a systems development project, requirements will be created that describe what the business needs (business requirements); what the users need to do (user requirements); what the software should do ( functional requirements); characteristics the system should have (nonfunctional requirements); and how the system should be built (system requirements).

Structured Analysis is a development method that allows the analyst to understand the system and its activities in a logical way.

It is a systematic approach, which uses graphical tools that analyze and refine the objectives of an existing system and develop a new system specification which can be easily understandable by user.

 

It has following attributes −

It is graphic which specifies the presentation of application.

It divides the processes so that it gives a clear picture of system flow.

It is logical rather than physical i.e., the elements of system do not depend on vendor or hardware.

It is an approach that works from high-level overviews to lower-level details

Structured Analysis Tools

During Structured Analysis, various tools and techniques are used for system development. They are −

  • Data Flow Diagrams
  • Data Dictionary
  • Decision Trees
  • Decision Tables
  • Structured English
  • Pseudocode

Requirement Elicitation

  • Elicitation is about seeking information about the software, the system, and the business.
  • One of the first tasks for the system analyst is to identify the primary sources of requirements.
  • All of the key stakeholders (the people who can affect the system or who will be affected by the system) must be included
  • Fact-finding involves answers to familiar questions: who, what, where, when, why and how (“5Ws and an H”)

Elicitation Techniques

There are a variety of elicitation techniques that can be used to acquire information, including:

  • interviews
  • questionnaires
  • observation
  • joint application development (JAD) and
  • document analysis/review.

Conducting the Interview

  • It is critical to carefully record all the information that the interviewee provides.
  • As the interview progresses, it is important that you understand the issues that are discussed.
  • Finally, be sure to separate facts from opinion

Questionnaires

  • A questionnaire is a set of written questions for obtaining information from individuals. Questionnaires often are used when there is a large number of people from whom information and opinions are needed.

Observation

Observation, the act of watching processes being performed, is a powerful tool to gain insight into the as-is system. Observation enables the analyst to see the reality of a situation, rather than listening to others describe it in interviews or JAD sessions

Question

  • What is the meaning of analysis? What is the purpose of the analysis phase of the SDLC?

Interviews

  • An interview is a planned meeting during which you obtain information from another person
  • The interviewing process consists of steps for each interview:
  1. Determine/select the people to interview
  2. Develop interview questions
  3. Prepare for the interview
  4. Conduct the interview
  5. Evaluate the interview.

Document Review

  • Document review can help you understand how the current system is supposed to work.
  • A good volume of records and reports are often available in many organizations, which provide useful information about the existing system.
  • You should obtain copies of actual forms and operating documents currently in use.
  • If the system uses a software package, you should review the documentation for that software

Observation

  • Observation, the act of watching processes being performed, is a powerful tool to gain insight into current operating procedures.
  • Observation enables the analyst to see the reality of a situation, rather than listening to others describe it in interviews or JAD sessions.

Questionnaires

  • A questionnaire is a set of written questions for obtaining information from individuals.
  • Questionnaires often are used when there is a large number of people from whom information and opinions are needed.
  • Questionnaires are commonly used for systems intended for use outside of the organization (e.g., by customers or vendors) or for systems with business users spread across many geographic locations.
  • Most people automatically think of paper when they think of questionnaires, but today more questionnaires are being distributed in electronic form, either via e-mail or on the Web.

Joint Application Development (JAD)

  • JAD is an information gathering technique that allows the project team, users, and management to work together to identify requirements for the system.
  • A JAD team usually meets over a period of days or weeks in a special conference room so that they are not interrupted.
  • All relevant issues are discussed and the needed information collected

Typical JAD Participants and roles

 

Structured Analysis

  • Structured analysis is a part of Structured Analysis and Structured Design (SASD) methodology.
  • Structured Analysis (SA) is a methodology for determining and documenting the requirements for a system.
  • Its purpose is to analyze users’ requirement, carry out functional decomposition of a system and represent the same through some standard graphical tools
  • For this some standard graphical tools and techniques are used. Data Flow Diagram (DFD), Data Dictionary, Decision Table, Decision Trees, ER Diagram, and State Transition Diagram (STD).

Data Flow Diagram

  • A data flow diagram (DFD) shows how data moves through an information system but does not show program logic or processing steps.
  • It is a technique that diagrams the system’s functions or processes and the data that pass among them without suggesting how they are conducted.

Basic elements of DFD

  • There are four major elements in the DFD language (processes, data flows, data stores, and external entities), each of which is represented by a different graphic symbol.

 

DFD Elements

  • A process is an activity or a function that is performed for some specific business reason.
  • A process receives input data and causes some transformation to the data (output).
  • A system may consist of a number of processes
  • In DFDs, a process symbol can be referred to as a black box, because the inputs, outputs, and general functions of the process are known, but the underlying details and logic of the process are hidden.

DATA FLOW

  • A data flow is a path for data to move from one part of the information system to another.
  • A data flow in a DFD represents one or more data elements or items.
  • The symbol for a data flow is a line with an arrowhead.
  • Every data flow must be connected to at least one process (either moving in or from the process).

DATA STORE

  • A data store is used in a DFD to represent data that the system stores because one or more processes need to use the data at a later time.
  • For instance, instructors need to store student scores on tests and assignments during the semester so they can assign final grades at the end of the term.
  • The flow from the data store usually represents the reading of the data stored in the data store, and the flow to the data store usually expresses data entry or updating.
  • Every data store is named with a noun. Two data stores cannot be connected by a data flow without an intervening process.

EXTERNAL ENTITY

  • An external entity is a person, department, organization, or information system that is external to the system, but interacts with it (e.g., customers, managers, student, bank, authorities).
  • External entities provide data to the system or receive output from the system.
  • An external entity must be connected by a data flow to a process, and not directly to a data store or to another external entity.
  • DFD entities also are called terminators. Systems analysts call an entity that supplies data to the system a source, and an entity that receives data from the system a sink.

Types of DFD

  • DFD are of two types, i.e. Physical DFD and Logical DFD.
  • The DFDs considered so far are examples of Logical DFD.
  • A Logical DFD specifies various logical processes performed on data. It does not specify information such as: who does the processing, where the processing is done, or on which physical device data are stored. The above facts are specified by Physical DFD.

Data Dictionary

  • The Data Dictionary describes all these elements of a system
  • A data dictionary, or data repository, is a central storehouse of information about the system’s data
  • An analyst uses the data dictionary to define or look up information about the system including the contents of data flows, data stores, entities, and processes
  • Attributes usually recorded and described in the data dictionary

Process Description Tools

A process description documents what the process does (processing steps and business logic) and provide additional information that the DFD does not provide.

The tools commonly used to describe processing logic include:

  • Structured English
  • Decision trees, and
  • Decision tables.

Structured English

Structured English uses short sentences to describe the work that a process performs clearly and accurately. When using structured English;

  • Use only the three building blocks of sequence, selection, and iteration. E.g. IF, THEN, ELSE, DO, WHILE …ENDDO.
  • Use a limited vocabulary, including standard terms and specific words that describe the processing rules
  • Selection statement:  iteration statementIF condition  WHILE condition

    THEN action 1  action

    ELSE action 2

    ENDIF  REPEAT action

    UNTIL condition

    Sequence statement

    action 1

    action 2

An example of Structured English which shows the “Assign Final Grade” process that was illustrated earlier is shown below:

  Input data flow class gradebook, grading details

Output data flow graded sheet

IF student mark > 69

THEN grade = A

ELSE IF student mark >  64

THEN grade = B

ELSE

grade = C

ENDIF

Decision Tables

A decision table is a logical structure that shows every combination of conditions and outcomes.

Analysts often use decision tables to describe a process and ensure that they have considered all possible situations. It consists of four sections.

 

  • How does a Chemical Tracking System decide whether to approve or reject a request?
  • Is the requester authorized to request chemicals?
  • Is the chemical available either in the chemical stockroom or from a vendor?
  • Is the chemical on the list of hazardous chemicals?

Is the requester trained in handling hazardous chemicals?

 

 

Entity Relationship Model

  • The data store notation in the DFD shows the existence of one or more groups of stored data. However, it does not give adequate information about the details of the data.
  • Data stores of a system are mostly related with each other. However, neither DFD nor the Data Dictionary shows the relationship between different data stores.
  • The details about the data stores and the relationships between them are shown by the ERD. The ERD is used for modeling of stored data.
  • The ERD is based on perception of the real world. Any real system consists of a collection of basic objects, called entities.
  • An entity is a “thing” or “object” for which data is collected and maintained. For example, each student of an educational institution is an entity.
  • Entities are described by their characteristics called attributes. Hence, an entity “student” may consist of some attributes such as student id, name, department, class, etc. A number of similar entities (i.e. say students) constitute an entity set.
  • Generally, there is at least one attribute called the primary key that uniquely identifies one entity from another in a set of entities.
  • An entity set can have more than one such attribute to identify an entity. All such attributes are called candidate keys from which one is chosen as the primary key.
  • The mapping cardinality and the degree of relationship describe the way the various entities of entity sets are related with each other
  • ERD uses certain notations to model stored data of a system.
  • Entity sets are shown by a rectangular box on the ERD. Relationships are shown by the diamond-shaped boxes. Attributes are represented by ellipses. A multi-valued attribute is represented by two concentric ellipses. Underlining an attribute indicates that it is a primary attribute.

 

 

You have reached the end of unit 2. Congratulations.

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