Download - Isad Chapter 1
-
7/29/2019 Isad Chapter 1
1/47
The System Environment
What is a SYSTEM? A composite of equipment, skills, techniques, and
information capable of performing and/or supportingan operational role in attaining specified management
objectives. Includes related facilities, equipment, material,
service personnel, and information required for itsinformation to degree that it can be considered a self-sufficient unit in its intended operational and/orsupport environment.
-
7/29/2019 Isad Chapter 1
2/47
FILE
Computer Processing Unit
Terminal
Computer System
-
7/29/2019 Isad Chapter 1
3/47
Theoretical View of System
Theoretical approaches to systems haveintroduced many generalized principles.
Goal Setting Defines what exactly the system
wants to do.System Boundary Concerned with system
structure and behavior.
Environment Anything outside the systemenvironment.
Subsystems Part of systems function.
-
7/29/2019 Isad Chapter 1
4/47
A GOOD system willbe made up ofhighly independentsubsystems withminimal flows
between them.
Minimizing flowsminimizes, in turncomplexity and simplifies
the system.
-
7/29/2019 Isad Chapter 1
5/47
Why is Systems Analysis
Necessary? To set-up the right procedures to ensure
that all organizations personnel have all
the data needed for their work. Systems Analysis provides understanding
of the existing system before system
design commences.
-
7/29/2019 Isad Chapter 1
6/47
Typical Information Systems
Human Resource System One importantsubsystem in most organizations is thepersonnel system which keeps personal detailsabout people organization. Typical Information
included is data about employees date of birth,addresses, marital status and medical histories.Personnel system also keep information onemployment histories, VL and SL records,position held and any special assignments.Records of skills, qualifications and specialcourses attended by employees are also storedin personal system.
-
7/29/2019 Isad Chapter 1
7/47
Customer or Client System The goal of thissystem is to provide service to the clients. Thereis a lot of variety but all follow a similar pattern.They usually begin with the client approachingthe organization with a specific request. Therequest is recorded and check to see ifrequested service can be provided. If it can,
arrangements are made within organizations toprovide the service. This may involve arrangingof some goods to be delivered or payments tobe made to the clients. Usually the client systemfollows up a requests to ensure that the service
is carried out and to answer any customerqueries about the service.
-
7/29/2019 Isad Chapter 1
8/47
Inventory Control System The primary goal ofinventory control system is to ensure that allnecessary parts are available at all times.
However, this does not mean that as many itemsas possible should be stored in the warehouse.Stored items do not cost money and do notgenerate any returns while stored. Thus aninventory system must maintain the minimum
possible number of items in store while ensuringthat needed items are always available. Adistinction can be made between two kinds ofinventory. One is an inventory of partspurchased by the organization for its internal useor to produce other products, while the other isan inventory of parts produced or purchased bythe organization for sale to its customer.
-
7/29/2019 Isad Chapter 1
9/47
Accounting System The 3 major subsystems
of accounting are:Accounts Receivable - subsystem includes
invoicing, credit checking, recording paymentsand sales, general analysis and reporting.
Accounts Payable - subsystem that is thereverse of Accounts Receivable
General Accounts Subsystem producesreports about the organizations assets and its
resources.
-
7/29/2019 Isad Chapter 1
10/47
Marketing System Marketing systempublicize the organization to its external
environment. This involves many
things, such as preparing information
about the services and disseminating it
to potential customers. Such activity
may include advertising, mailouts or
simply visiting the customer.
-
7/29/2019 Isad Chapter 1
11/47
Systems Design
(definition) The complete plan for producing
an operational system, which
includes problem description,algorithm, development,
flowcharting, coding, program
debugging and documentation.
-
7/29/2019 Isad Chapter 1
12/47
Linear Cycle ProblemDefinition
Feasibility
StudySystems
Analysis
Systems Design
HLAD
Detail
Design
Development
Implementation
Maintenance
Post ImplementationReview
System Implementation
Working System
-
7/29/2019 Isad Chapter 1
13/47
Stage DesignFeasibility
Study
Define
stages
Problem
Definition
Feasibility
Study
Systems
Analysis
System Implementation
System Design
Stage 1
-
7/29/2019 Isad Chapter 1
14/47
Alternative Life Cycles
Evolutionary Design does not assume that we
can subdivide the problem into distinct and
loosely-coupled phases and design the system
in one pass through these phases. The systemis developed gradually. We developed a system
part and learn more about the problem from the
operation of that part. With the knowledge
gained from this operation we can define thenext part to be developed. This part is being
developed and the process continues.
-
7/29/2019 Isad Chapter 1
15/47
Imprecise Systems
Imprecise systems occur when it is not
possible to start with a set of precise
system requirements. This often occurs in
the organizations that are just starting withcomputers or in novel applications where
there is no previous experience. Instead it
is more appropriate to develop the systema little bit at a time, learning about system
capabilities as one goes along.
-
7/29/2019 Isad Chapter 1
16/47
Decision Support Systems
The problem here differs from that found in
imprecise systems, where it is clear that
the system will eventually do what is
expected to it, even though it is not clearhow the system work. Decision support
systems have a further degree of
uncertainty because it is not clear whethera computer can be used at all to solve
problem.
-
7/29/2019 Isad Chapter 1
17/47
Evolutionary Design Method
User
Suggestion
Pilot system
developed
in conjunction
with user
Design/
Program/ Test
Transfer of ownership (usually
a gradual activity)
Through out the design
Process.
Conversion
Operation of
final product
Inception
Initial Grouping
Mutual Progress
Conversion
Maturity
-
7/29/2019 Isad Chapter 1
18/47
Prototypes
Prototyping differs from evolutionary
design in one significant way. A prototype
is often considered to be a model of a
proposed system. It is built to illustrate thefeasibility of a new system and then
virtually thrown away. The new system is
then built from scratch.
-
7/29/2019 Isad Chapter 1
19/47
Advantage of Protyping
More clearly identify system objectives
More clearly identify critical problems
More clearly identify logical solutions
-
7/29/2019 Isad Chapter 1
20/47
Prototyping in Systems
DevelopmentSystem
Problem
Evaluate
Feasibility
Prototyping
No
Yes
Identify
Critical
Logical
Operation
Suggest
Alternative
Logical
Solutions
Evaluate
Alternative
Physical
Implementation
Detailed
Designed
Implementation
Linear Prototype
Development Cycle
-
7/29/2019 Isad Chapter 1
21/47
Implementing Evolution Design and
Prototyping
Evolutionary design and prototyping call forspecial development methods. These life cyclesrequire experimentation and continual change todevelop systems. We do not want a situationwhere every change requires us to throw awaywhat has been done so far and start again, sowe require development techniques that allowus to make changes or add new components
without an ordinate amount of programming.The alternative cycles become very attractive ifthis can be done.
-
7/29/2019 Isad Chapter 1
22/47
Information Systems Architecture
An ISA is a conceptual blueprint or plan
that expresses the desired future structure
for information systems in an organization
It provides a context within which
managers throughout the organization can
make consistent decisions concerning
their information systems
-
7/29/2019 Isad Chapter 1
23/47
Benefits of Information Systems
Architecture
Provides a basis for strategic planning of IS Provides a basis for communicating with topmanagement and a context for budgetdecisions concerning IS
Provides a unifying concept for the various
stakeholders in information systems. Communicates the overall direction for
information technology and a context fordecisions in this area
Helps achieve information integration when
systems are distributed (increasing importantin a global economy) Provides a basis for evaluating technology
options (for example, downsizing anddistributed processing)
-
7/29/2019 Isad Chapter 1
24/47
ISA Framework Components
Data The What of the information system
Process The How of the information system
Network
The Where of the information system People
Who performs processes and are the source and receiver ofdata and information.
Events and Points in time When processes are performed
Reasons Why: For events and rules that govern processing
-
7/29/2019 Isad Chapter 1
25/47
Six roles or perspectives of the Data,
Process and Network components
Business scope (Owner)
Business model (Architect)
Information systems model (Designer) Technology model (Builder)
Technology definition (Contractor)
Information system (User)
-
7/29/2019 Isad Chapter 1
26/47
Data Flow Diagrams
DFD symbols
External entities (sources and sinks)
Data Stores
Data Flows
Processes
Types of diagrams
Step by step approach
Rules
-
7/29/2019 Isad Chapter 1
27/47
Some Rules for External
Entities External people, systems and data
stores
Reside outside the system, but
interact with system
Either a) receive info from system,
b) trigger system into motion, or c)
provide new information to system
e.g. Customers, managers
Not clerks or other staff who simply
move data
External
Entities
-
7/29/2019 Isad Chapter 1
28/47
Some Rules for Data Stores
Internal to the system
Data at rest
Include in system if the systemprocesses transform the data
Store, Add, Delete, Update
Every data store on DFD shouldcorrespond to an entity on an ERD
Data stores can come in many
forms: Hanging file folders Computer-based files
Notebooks
-
7/29/2019 Isad Chapter 1
29/47
Some Rules for Data Flows
Data in motion, moving from
one place to another in the
system
From external entity (source) tosystem
From system to external entity
(sink)
From internal symbol to internalsymbol, but always either start
or end at a process
Data Flow
-
7/29/2019 Isad Chapter 1
30/47
Some Rules for Processes
Always internal to system
Law of conservation of data:
#1: Data stays at rest unless
moved by a process.
#2: Processes cannot consume or create data Must have at least 1 input data flow (to avoid miracles)
Must have at least 1 output data flow (to avoid black holes) Should have sufficient inputs to create outputs (to avoid
gray holes)
-
7/29/2019 Isad Chapter 1
31/47
Processes Logical process models omit any processes that do
nothing more than move or route data, thus leaving the
data unchanged. Valid processes include those that:
Perform computations (e.g., calculate grade point
average)
Make decisions (determine availability of ordered
products)
Sort, filter or otherwise summarize data (identify
overdue invoices)
Organize data into useful information (e.g., generate
a report or answer a question)
Trigger other processes (e.g., turn on thefurnace orinstruct a robot)
Use stored data (create, read, update or delete a
record)
-
7/29/2019 Isad Chapter 1
32/47
Types of Diagrams
Context Diagram
A data flow diagram (DFD) of the scope of an
organizational system that shows the system
boundaries, external entities that interact with the
system and the major information flows between the
entities and the system
Level-O Diagram
A data flow diagram (DFD) that represents a systemsmajor processes, data flows and data stores at a high
level of detail
-
7/29/2019 Isad Chapter 1
33/47
Figure A
Context diagram of Hoosier Burgers Food ordering
system
-
7/29/2019 Isad Chapter 1
34/47
Figure B
Level-0 DFD of Hoosier Burgers food ordering system
-
7/29/2019 Isad Chapter 1
35/47
Creating Data Flow Diagrams
Creating DFDs is a highly iterative process of gradualrefinement.
General steps:
1. Create a preliminary Context Diagram
2. Identify Use Cases, i.e. the ways in which users mostcommonly use the system
3. Create DFD fragments for each use case
4. Create a Level 0 diagram from fragments
5. Decompose to Level 1,2,6. Go to step 1 and revise as necessary
7. Validate DFDs with users.
-
7/29/2019 Isad Chapter 1
36/47
Data Flow Diagramming Rules
General
Specific rules to
Symbols
Context Diagram
Level 0 and lower decompositions
Balancing across levels
-
7/29/2019 Isad Chapter 1
37/47
DFD RulesGeneral
Basic rules that apply to all DFDs
Inputs to a process are always different than
outputs
Objects always have a unique nameIn order to keep the diagram uncluttered, you can
repeat data stores and sources/sinks on a diagram
-
7/29/2019 Isad Chapter 1
38/47
DFD RulesSymbols
Process
No process can have
only outputs (a
miracle)
No process can have
only inputs (black
hole)
A process has a verb
phrase label
Data Store
Data cannot be moved
directly from one store to
another
Data cannot move directlyfrom an outside source to a
data store
Data cannot move directly
from a data store to a data
sink Data store has a noun
phrase label
-
7/29/2019 Isad Chapter 1
39/47
DFD RulesSymbols (cont)
Source/Sink
Data cannot move
directly from a source
to a sink
A source/sink has a
noun phrase label
Data Flow
A data flow has only one
direction of flow between
symbols
A fork means that exactlythe same data goes from a
common location to two or
more processes, data
stores or sources/sinks
-
7/29/2019 Isad Chapter 1
40/47
DFD RulesSymbols (cont)
Data Flow (Continued) A join means that exactly the same data comes from
any two or more different processes, data stores orsources/sinks to a common location
A data flow cannot go directly back to the sameprocess it leaves
A data flow to a data store means update
A data flow from a data store means retrieve or use
A data flow has a noun phrase label
-
7/29/2019 Isad Chapter 1
41/47
DFD RulesContext Diagram
One process, numbered 0.
Sources and sinks (external entities) assquares
Main data flows depicted No internal data stores are shown
They are inside the system
External data stores are shown as externalentities
-
7/29/2019 Isad Chapter 1
42/47
Decomposition of DFDs
Functional decomposition
Act of going from one single system to many
component processes
This is a repetitive procedure allowing us to providemore and more detail as necessary
The lowest level is called a primitive DFD
Level-N Diagrams
A DFD that is the result ofn nested decompositions ofa series of subprocesses from a process on a level-0
diagram
-
7/29/2019 Isad Chapter 1
43/47
DFD RulesBalancing DFDs
When decomposing a DFD, you must conserveinputs to and outputs from a process at the nextlevel of decomposition. This is called balancing.
Example: Hoosier Burgers In Figure B, notice that there is one input to the
system, the customer order
Three outputs: Customer receipt
Food order Management reports
-
7/29/2019 Isad Chapter 1
44/47
DFD RulesBalancing DFDs
Example (Continued)
Notice Figure B. We have the same inputs
and outputs
No new inputs or outputs have beenintroduced
We can say that the context diagram and
level-0 DFD are balanced
-
7/29/2019 Isad Chapter 1
45/47
Figure C
An unbalanced set of data flow diagramswhy?
(a) Context diagram (b) Level-0 diagram
-
7/29/2019 Isad Chapter 1
46/47
DFD RulesBalancing DFDs
An unbalanced example, Figure C
In context diagram, we have one input to the
system, A and one output, B
Level-0 diagram has one additional data flow,C
These DFDs are not balanced
-
7/29/2019 Isad Chapter 1
47/47