Transcript Introduction to Lifecycle - Manchester Metropolitan University

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
A system is defined by its boundary
Environment
System
Boundary
The system boundary sets it apart
from its environment
Systems
Different observers will view a system in a different way
There may be a different physical
context – e.g. CD Hotels
Systems
Different 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
Systems
Different observers will view a system in a different way
Both of these situations can cause
problems for the systems analyst
Systems
A system will consume resources from its environment
Environment
System
These may be physical or
conceptual
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
There will be a Goal
We are interested in information
Systems
The environment may be static
Environment
System
Or it may be dynamic
Magnitude and rate
of change are
important
Systems
A system must be able to change to match its environment
Environment
System
Change – To achieve its goal
Change – By reconfiguration
of components/resources
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
Practical Solutions
Redesign the system
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
Data
Process, Format
or
Transformation
Information
• ‘One person’s data is another person’s
information’
McCleod, 1998
Communication
• General Communications Channel
Source
Destination
Message
Transmitter
(encoder)
Noise
Received
Message
Channel
Signal
Signal +
Noise
Receiver
(decoder)
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
2
5
1
6
4
3
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
2
5
1
6
4
3
7
It is clear that we cannot develop any
part of the system in isolation
Structured Methods
User
Requirements
Existing Physical
System DFD
Convert to
Logical View
New Logical
System DFD
Repository
Repository
Existing System
ERD
New System
ERD
We therefore need to introduce a
certain amount of iteration into our
development process
Technical
Options +
Constraints
New Physical
System
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