Notes Chathura

8/9/2019 Notes Chathura

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Requestparts

PurchaseOrder

STRUCTURED SYSTEM ANALYSIS AND DESIGN METHOD

Structured system analysis and design methodology is a system approach to the analysis and design of information systems SSADM was produced for the CCTA, a UK government office concern with a use of technology in government , from 1980 onwards.

System design methods are a discipline within the software development industry which seek toprovide a frame work for activity and capture, storage, transformation and distribution of informationso as to enable the economic development of computer system that fit for perhaps.

SSAD is a waterfall method which an Is design can be arrive at SSADM can be tough torepresent a pinnacle of the rigorous document let approach to system design and contrast with rapidapplication methods such as DSDM.

General system conceptsA set of connected things or parts that form a whole together to achieve a a common goal, can

be defines as a system. The objectives of a system demand that some output is procedure as a result of processing suitable inputs.

inputs proces outputs

A PURCHASING SYSTEM

A purchasing system orders goods suppliers. It keeps list of suitable suppliers, their products, leadtimes, minimum quantities & etc. Inputs to the purchasing system are requested for a parts, theprocessing is to select the most suitable supplier , negotiable rates, arrange delivery times & dates m theoutputs are purchase orders, notifications to the ware house that the parts have been ordered.

process

WareHouse

Purchasing

Department

Supplier

Notification of purchasing order

System Boundary


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An order processing system

Order

Parts pick list

request order purchase order

Notification info

CustomerSales OrderOffice

Ware

House

Purchase Dept.

Supplier


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DATA FLOW DIAGRAMS

DATA FLOW DIAGRAM SYMBOLS

1. External entity

2. Process

3. Data store

4. Data flow Quotation Details

External Entity

The fundamental purpose of the symbol which is either a source of data ( An inquire) or a sink ( Aquotation) is to indicate that whatever happens at the end of the data flow. It is not the concern of theactivities been studies may be people, departments, functions, or other groups external to the area

customer

M


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being described by the DFD. An external entity cannot directly access a data store. A process can existbetween an external entity and a data store.

Process

In a DFD the rectangle implies shows that some activity takes place, transforming theinput data.

There must be no increase or decrease in the data as a result of processing. If the totalof the inputs does the outputs in all process the DFD is incomplete.

DATA STORES AND DATA FLOWS

There are only two justifications for data stores in any system. One is that data exists which will berequired frequently for output. But would be costly & time consuming to input each time. Thereforereferenced files are created. The second reason is that data exists which is not required currently by theprocess but which will be required either in another or at a later date. It is not always necessary to nameflows to & from stores for e.g. When validating customer info. Again the customer data store it is onlynecessary to show a data flow line from the data store to the process. Data store cant communicatewith another data.

Levels

HOW MANY LEVELS?

There are no rules about the num of the levels of the DFD used. This is holy dictated by the application &the analyst. In some cases a single DFD will show all what is needed. In other cases 2,3 or more levels of DFD may be necessary.


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2 DoctorauthorizePrescription

Request a prescription

Pres. request

1 Surgery Prescription info 1 prescription details

Extract Details or

Prescription

Prescrption Details

Authorized Prescription

Patient

Patient


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1.1 Reception

1.2 Reception

Valid Person

Personal

details

APPLYING FOR A MEMBERSHIP LEVEL 2

Title

1 Produce Membership Card

Request membership validate personal

details

Produce D1 Members Details

Membership card

REVIEVING THE FIRST LEVEL DATA FLOW DIAGRAM

1. The complete life of each data flow has been record.2. Each data store has a flow going into &one coming out. (Not necessarily from the same process.)

PersonPerson

Member

Completedapplicationform


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Work station

Service Car

BUSINESS ACTIVITY MODELLINGWhen investigating the information technology requirements for a new system a definition of requirements is of better quality if it is based only why the knowledge of the business environmentwithin which the users operate.

The definitions of requirement are improved whether if the analyst understands not only what the usersdo, why they do it & how different users business activities are interrelated. The business activity model(BAM) is a meets of documentary & analyzing those activities which are essential for the business tomeet specific objectives. It enables the analyst to understand the overall business & developrequirements to ensure that the new computer system will support the attainment of the businessobjects.

BUSINESS ACTIVITY MODEL DIAGRAM

SUPPLIER New Parts BUYER spare parts Parts store

obtain spare parts

customer car Reception cars for service

Collect car

Resource flow

The business activity model should contain 4 components

1. The business perspectives Sharing why the business does what I does

2. The business activities & their interactions3. The business events indicating when business activities are carried out4. The business rules

Defining how activities should be carried out


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DEALING WITH THE USER

The analyst needs to keep in mind the fact that at all levels has a job to do. The amount of timethat they can usually allocate to describing their work, checking that the analyst has correctly

understood it & generally working with the analyst to be very limited.

However resent user centered approach to the system development requires appropriate usersto be allocated to the development team or considerable proportion of their time. ( Policies even fulltime for a short period.) this can be very effective provided that the user does not also have the wholeof their usual job to perform at the same time.

MISSING THE OBVIOUSA user knows their functions in the existing system & the often considers it to be obvious.

However it may not be obvious to the analyst, who will need care & fact to obtain relevant information.The difficulty in trying is in trying in a very short time to understand what is done & why. The peoplewho operate the system are completely familiar with it, where as the analyst is not. They know what isimportant and what is desirable. (Nice to have)

The analyst should try to identify the important parts of the policy been implemental. He or shecannot expect to receive a clear details & accurate account of precisely what is done, why & with whatproperties.

INSTANT DESIGNWhile the analyst is taking to people listen & recording what they say his or her mind will be

busy pigeon holding. The analyst should take great care at the early stage. He or she should not commit

anyone to a particular part & should make no promises or suggestions. The analysts usually just not haveany authority to make decisions at this stage regarding the future development.

TIMES OF REFERANCE

Before an analyst can start the investigation he or she requires the investigation he or sherequires a statement of what needs to be done. This statement is called terms of reference. It sets outthe,

1. Objectives of the investigation2. Boundaries3. Allowable expenditure & other resources available4. Time by which it should be completed.5. Method of presenting the results


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1. OBJECTIVES OF THE INVESTIGATION

The initial study I is a miniature investigation of its own which high lights areas that need a more detailinvestigation of its own, which highlights the arias that need a more detail investigation & also providesrough cost & benefits expected if a new system were implemented. This information can be dangerous& misleading during the detail investigation. The analyst must not think solutions until the work of analysis is complete. However the feasibility report spells out the basic objectives that should be met bya new system & this helps the analyst to determine the user requirements.

2. Boundaries

The boundaries of an investigation are usually stated as departments, groups or functions thatare to be studied or sometimes excluded from the study. If the analyst can be given a list of thosepeople or groups who provide input to the aria to be investigated, and a list of those who receiveoutput from (e.g. The sources and sinks) then or she has by implication been given the boundaries .Thepeople or department that are the sources of input data and those that receive the output, sinks (A sinkIs a person or place that receives the output), are outside the area to be investigated. Everyone andeverything are in between the domain of study however this statement assumes that the analyst canidentify quite precisely what data flows in to an out of the domain of the study. Sometimes this is nottrue and as the investigation progresses and problems and requirements are identified, what initiallyappeared to be a source or a sink may need to be brought within the system boundary.

COST and TIME LINES

Cost and time are a normally two sides of a same coin.(D1) Cost is the number of person days atthe going rate. b

Not all investigations are carried out by one person full time if a particular investigation iscarried out in this way a time scale for completion will be the number of person days and the cost willbe that number multiplied by the current person day rates.

REQUIREMENT CATALOGUE

The analyst should build of the details of the requirements for the new system throughout theinvestigation process. This can be in the form of a requirement catalogue. The requirementcatalogue is the central repository for information about requirements. The format will bedependent on the case tool which is been used to manage the Catalogue but At least thefollowing information should be recorded to each requirement.


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1. Requirement id/number

2. Requirement name

3. Business activity

5. Source Person document

6. PRIORITY(high, low, optional)

7. Owner person with the responsibility who negotiates about the requirements

8. Requirement type - functional and

(Find out the functional and non functional requirements)

9. Benefits expected implementation of this requirements

10. Comments /suggestions

11. Related documents

12. Related requirements

MODIFYING THE TERMS OF REFERANCE

It is by no means uncommon for analyst to discover that some of the terms of reference needto be modified in the light of detailed knowledge. It is therefore better to limit the initial termsof reference to a statement of boundaries and timings. Then after the initial investigation theterms of reference can be expanded to include new objectives and widen the scope of fullinvestigation.

METHODS OF INVESTIGATION

The first step in fact finding is to study background information on the area to be investigated.Business activity modeling gives the analyst a sound understanding of the overall businessenvironment .other useful information includes


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1. How the organization is structured, the relationships between various departments whoholds the key responsibilities their style of management and their interest in the currentinvestigation.

2. Previous studies that may have been carried out and their outcome, were the resultsaccepted or turndown, and why.

Having studies the background information, the analyst is ready to proceed with theinvestigation. A number of methods can be used to collect facts; the analyst must choose whichmethod most suit the investigation and time scale.

methods are observation, record searching , special purpose recording , sampling

, questioners, interviewing, workshops,

[Functional and non functional requirements

Simultaneous users doing two different actions in the same application at a given time

Concurrent users - doing the very same action in an application at the same time]

Entity Analysis

An entity is a thing which holds information about an organization. Entity modeling is a techniqueshowing relationships between entities. Entity analysis is the process by which the model is developedand identifies the underline structure of the data and relationships of those data.

The diagram produce from entity modeling is called entity relationship diagram (ERD).

When is entity analysis performing?

Entity analysis is performs at two stages during the analysis phase of a system.

1. During analysis of the existing system, to aid the analyst understanding of it.2. In conjunction with relational data analysis to produce a model of the required data structure

of the new system.


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EntitiesAs defined above an entity is a thing about which the organization wants to hold information. Entitiesmay be physical things such as

1. Customer

2. Invoice3. Product4. Supplier5. Employee6. Training course

Or conceptual things related to the business area such as

1. Salary grade2. Sickness history3. Project

AttributesAll the entities have attributes. They are data that describes or qualifies the entity. In the entityemployee attributes could be

1. Employee no2. Employee name3. Employee address4. Employee department5. Employee salary

Entity occurrenceAn entity has number of occurrences. If there are 200 employees in an organization there will be 200occurrences of the entity employee. Each individual occurrence must have a unique identifier (a key)

Employee no Name Address dept salary

H001 Perera No. 5, Colombo HR Rs.50,000

Is one occurrence of the entity employee with a unique key of employee number.

RelationshipsThe relationship between two entities describes the way in which occurrence of one entity is linked to,or influence by occurrence of another. For e.g. a department may have 0, 1 or many employees but each


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employee will relate to only one department. (In this example where the business rule is that anemployee will only work in one department.)

NotationEntity description the entity name is always in the singular within a rectangle

Relationship a relationship between two entities is shown as a line.

Producing an entity relationship diagram

Selecting initial entitiesAn entity can be identified by looking at existing files and documents where there is a uniquekey(identifier) this will be a candidate for an entity an employee has a unique employee no, an

Invoice has a unique no, etc.

In a library example a member (borrower) has a unique membership number and a book has a uniquebook no.

There will also be a topic catalogue where each topic is unique, an author catalogue where each has aunique code, a reservation facility where the borrower number and the book number are recorded,therefore first set off entities identifies for the library is

1. Borrower2. Book3. Author4. Topic

5.

ReservationAs with data flow diagrams entity modeling is an iterative process. Not all entities may be located at thefirst attempt. If there is any doubt about whether something is an entity or not , it should be included.The model will go through many stages of checking, where the redundant entities can be removed.

Placing entities in a grid

BORROWER BOOK AUTHOR TOPIC RESERVATIONBORROWERBOOK *AUTHORTOPIC *RESERVATION


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Entity Life Histories (ELH)

Entity life histories look at a system providing a means of representing how entities change within asystem with the passage of time. ELH start with the creation of an entity occurrence, record the

sequence of changes that take place during its life within the system and end with its removal from thesystem.

When are ELH s produced?It should be used during logical system design to validate the completeness and correctness of dfds anddata analysis and again alongside analysis of access requirements to ensure that all events which causechanges to entities are considered.

Concepts and terminology

Update processers

Processors can be divided into two types.

1. Those which change the systems data2. Those will simply referencing

They are called update inquiry/retrieval processors. ELH will concern with update processors only. Thefollowing diagram represents and updates process in a DFD. Update processing within the processcreate new customer may include

1. A validity test of the format of the input data flow.2. A check that the customer is not already on the file.3. Creation of a new occurrence of the customer entity

D. 01

cutomer

create a new customer diagram

Sales dept Create new

customer


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EventsAn event is anything that activates (triggers) an update process. It may be the receipt by the process of aparticular data flow or it may be the arrival of a particular pointing time. Example: end of day, end of month, yearend which is recognized by the system.

EffectsA single event may cause more than one entity to change. Eg. It may have more than one effect. Aneffect can be

1. A creation of deletion of entity occurrence2. Changes of the attributes of the entity occurrence3. Creation or deletion of relationships4. A combination of the above

Sub eventsA single event may result in different effects depending on the condition of data when the event occurs.

In such cases the different effects are said to be caused by sub events, which are the combination of anevent and the condition of the data within the system at the time that the event take place.

E.g. Ammendments ofdetails

If the customer not on file insert new customer, otherwise amend details

Entity life history notation

Sales DepAmend

Customer

Customer


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General structureAn ELH is a pictorial mean of represent ting events that can affect the life of an occurrence of an entity,from its creation within the system to its deletion from the system. The following diagram shows thegeneral structure of an ELH.

The events followed the sequence create, amend, delete from left to right in the diagram

General structure of an entity life history

The top box always containing the name of the entity lower level boxes represents events that canhappen during its life within the system.

The diagram is a hierarchy each lower level box will only be related (connected) to one higher level box.The higher level box represents a sequence made of the lower level boxes connected to it. It is usual toconsider the most common sequence of events first, adding in abnormal events once an initial diagramhas been drowned. The structure diagram is based on three constructs

1. Sequence2. Selection3. Repetition

29.11.2009

Eventsassociatedwith entity A

Events whichcourse entity of A to be created

Events which causeentity occurrence of Ato be mended

Events which courseentity occurrence of A to be deleted


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SequenceAs per the create new customer diagram new customer authorization is the first event to have an effecton customer follows by customer amendments ,followed by customer deletion, followed by monthlyarchive these events always happen and always in that sequence.

SelectionThe symbol O denotes selection

Following diagram states that a detail changed event either a credit limit change or an address change

RepetitionThe star (*) on the top right hand corner of a box denotes repetition. The diagram states that the eventcustomer amendments consist of 0,1 or many detail changes.

Amendments

Detail Change *

Credit Limit Change Address Change


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Diagram

Q- Briefly explain the uses of en entity life history?

Optional eventsAn optional event is one which may or may not happen. This situation represents on the followingdiagram is that customer reinstatement may or may not occur

Customer

New customer

Authorization

Amendments Deletecustomers

Archieve

Detail changes *

Credit limit Address change


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Missed notes typed late

An entity is recognized as a physical thing that has a unique key. The relationship can be identified bythe connection between the entities.

Identifying additional characteristics

Named relationships

The relationships between two entities should be named in both directions

The write of written by

Optional relationships

A book can exist without being issued, the membership with issue is zero, one or many. However anissued cant exist without a book. Use a dotted line to show optional

The relationship between two entities can be divided as

1. One to one2. One to many

author Book


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3. Many to many

For every pair of entities connected on the diagram tow questions are asked

1. Can the occurrence of the author be associated with more than one occurrence of book2. Can the occurrence of book be associated with more than one occurrence of author

One to one relationship

Many to many relationships

If an author writes several books, the answer to the first question is? YES

If a book is only ever written by one author the answer is NO

(To keep it simple assume that a book is written by only one author)

The many end is represented by a crows foot

As shown in the first diagram there is one to one relationship in the library example. As in the diagram 2would mean that all authors only ever write one book.

Author Book

Author Book

Author Book


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The relationship between book and borrower is many to many. A book can have many borrowers and aborrower can borrow many books.

Q. EXPLAIN HOW ENTITIES AND THEIR RELATIONSHIPS ARE IDENTIFIED DURING THE INVESTIGATION OFTHE SYSTEM.

Exclusive relationships

Exclusive relationships describe either or situation. This is indicated by an arc. Which show

A relationship defines the association between a master entity and a detailed entity. for each masteroccurrence it should be possible to access all details of that master the customer is the master and orderthe detail given a customer number can be accessed.

MASTER

MASTER/DETAIL

DETAIL

EMPLOYEE

WEEKLY PAY MONTHLY PAY

CUTOMER

ORDER

PRODUCT


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In order/ product order is that master and product the detail given on order number all products in thatorder can be accessed.

An entity can therefore be a master in one relationship and a detail in author.

EXCLUSIVE DETAILS

EMPLOYEE

WEEKLYPAY

MONTHLPAY

CUSTOMER SUPPLIER

INVOICE

Documents

Notes Chathura