Further Systems Analysis

Plan

• Introduction

• Structured Methods– Data Flow Modelling– Data Modelling– Relational Data Analysis– Further Data Modelling– Further Systems Analysis Topics

Information and Systems

…and Information Systems

Systems

• There is no universally accepted definition of a system

• Properties that are generally considered part of a good definition– An organised or complex whole– An entity that consists of independent parts– These parts are affected by being part of the system

and are changed by being removed from the system– A collection of related activities working together to

achieve a common objective– An assembly of parts that have been identified by an

individual as being of special interest

Systems

System

A system is defined by its boundary

The system boundary sets it apart from its environment

Environment

Boundary

SystemsDifferent observers will view a system in a different way

There may be a different physical context – e.g. CD Hotels

SystemsDifferent observers will view a system in a different way

It may be that the difference is more conceptual It’s the same system but it is

described using a different set of symbols

SystemsDifferent observers will view a system in a different way

Both of these situations can cause problems for the systems analyst

Systems

System

A system will consume resources from its environment

These may be physical or conceptual

Environment

A system will also produce some output

Biological Systems

• Frogs Inputs

Outputs

Natural Systems – Goal unclear

Man Made Systems

• Inputs– Physical Resources– People– Information– Money

• Outputs– Physical Goods– People– Information– Money

There will usually be some transformation

We are interested in information

There will be a Goal

Systems

System

The environment may be static

Or it may be dynamic

Environment

Magnitude and rate of change are important

Systems

System

A system must be able to change to match its environment

Change – To achieve its goal

Environment

Change – By reconfiguration of components/resources

System

Impact on Development

• We must be aware of the system’s environment– Static/Dynamic– Rate of change

• The system must be able to – React to change– Reduce the effect of change

Law of Requisite Variety

• A system must be as complex as the environment in which it operates

• Therefore it must be able to reconfigure it’s resources to react to environmental changes

SystemSystem

Practical Solutions

System

Redesign the system

Add new components to the system Create Adaptive Systems

Information Definitions• ‘Information is data which has been processed in such a way that it

has meaning to the person who receives it, who may then use it to improve the quality of decision making.’

CIMA Information Management Study Text

• ‘‘Information’ refers to the aggregation of data that - when it is interpreted and understood - provides systems users with knowledge of some kind.’

Edwards et al., The Essence of Information Systems

• ‘Information is raw data converted into a form to enable the user to make a decision in response to a business need.’

Thomas and Ballard, Business Information

• ‘Information is data that have been processed in such a way as to be useful to the recipient.’

Rowley, Strategic Management Information Systems and Techniques

Information

• Structure– Data is brought together to have some

meaning

• Processing– The data must be processed to give it

structure

• Communication– Information should communicate something to

the recipient

Information - Structure

• See TopDog examples

Information - Process

• In order to become information, data must undergo some form of Transformation, Processing or Formatting

• ‘One person’s data is another person’s information’

McCleod, 1998

InformationDataProcess, Format

orTransformation

Communication

• General Communications Channel

Source

Transmitter(encoder) Channel

Receiver(decoder)

DestinationNoise

Message

Signal Signal +Noise

ReceivedMessage

Information

• Structure• Processing• Communication

• Similar properties to systems• In order for information to exist there must be a

system to produce it• We control information by systems development

Review of SAD

The Problem of Development

• Development views of the system– System development is complex problem– We handle complexity by dividing the problem

• Process View• Data View• Dynamic View

Information System Architecture

1

2

3

4

5

6

7

1. Users

• Users send commands and instructions across the user interface

• Users send and receive data across the user interface

• The interface will also implement security controls (e.g. log in passwords etc)

2. User Interface

• How do we present information to our users?

• How do we collect data?

• UI may be written in languages such as Visual Basic

• May even be written in HTML with scripting languages

3. User Interface

• Technology Used – HCI

• Usability Issues – Process and data Design

• Navigation – State Transition Diagram

• Design – GUIIN real systems People and Paper also form part of this interface (e.g. phone banking)

4. Processes

• The business processes are described using DFDs and other models (ELH, STD).

• They will be implemented in a programming language such as Visual Basic, Java, C++

• Should keep their implementation separate from the GUI

5. Data Interface

• There is an interface between the business processes and the data

• This is often implemented using SQL (structured query language)

• If a file system other than an RDB is used then this interface must be implemented by some other means.

6. Database

• The database is defined in the data model• Described in the process model

– via data dictionary

• Usually implemented in a Relational database– Oracle, Access, MySQL

• May also be implemented as paper files or electronic files (e.g. HTML)

7. System Boundary

• Defines the scope/context of the system– Identified in the DocFD and Context Diagrams

• All access to the system should be via the user interface

• Some users may be other systems

• All interfaces need to be carefully defined to avoid security, and other problems

Development Process

• What is the scope/context of the system?

• What must it do? What are its outputs?– Requirements Gathering – Rich

Pictures/DFDs

• What Processes are needed to do it?

• What data do the processes require?– Requirements Analysis – DFDs/ERDs

Development Process

• How do we store the data (relational DB)?– Database Design - Normalisation

• How will the users use the system?– Interface Design – State/Transition Diagrams

Information System Architecture

1

2

3

4

5

6

7

It is clear that we cannot develop any part of the system in isolation

Structured Methods

Existing System ERD

Repository

Existing Physical

System DFD

New System ERD

Repository

New Logical System DFD

Convert to Logical View

User Requirements

Technical Options +

Constraints

New Physical System

We therefore need to introduce a certain amount of iteration into our development process

The End

• Have a good one…

References

• Whiteley, D. (2004) Introduction to Information Systems, Palgrave, 2004.

• Lejk, M. and D. Deeks (2002) Systems Analysis Techniques, Addison Wesley 2002

• Mason, D. and L. Willcocks (1994), Systems Analysis, Systems Design, Alfred Waller, 1994.

References

• Yeates, D. and T. Wakefield (2004) Systems Analysis and Design, FT/Prentice Hall 2004

• Gane, C. and T. Sarson (1979) Structured Systems Analysis, Prentice Hall, 1979

• Eva, M (1994) SSADM Version 4: A users guide, McGraw hill, 1994

References

• DeMarco, T. (1979) Structured Analysis and System Specification, Yourdon, 1979

• Royce, W. (1970) Managing the development of large software systems, In: Proceedings of IEEE WESCON, 1970 pp1-9.

• Connolly, T. and C. Begg (2000) Database Solutions, Addison-Wesley, 2000