Download Systems Analysis

DEPARTMENT OF INFORMATION STUDIES
LIS1510
Library and Archives Automation Issues
Systems Analysis
Andy Dawson
Department of Information Studies, UCL
(University of Malta 2010)
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
What we will be looking at today
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The lifecycle concept
The need for good analysis
Describing the system
Identifying the needs
Practical exercise – process modelling
Second coursework issued
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
The system life cycle (from yesterday)
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Analysis
Design
Implementation
Evaluation
• Decay
• Replacement
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
The systems development lifecycle
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Strategic study
Feasibility study
Physical systems analysis
Logical systems definition
Logical systems design
Physical systems design
Implementation
Maintenance
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Or more simply
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(Requirements) analysis
Design
Implementation
Maintenance
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
The PARIS model
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Plan
Ask
Record
Interpret
Specify
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
As we said yesterday...
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Why do so many systems seem to “fail”?
Misapprehension
Miscommunication
Misinterpretation
Misidentification
Misrepresentation
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
The role of Systems Analysis
• Systems analysis allows/helps us to:
– identify systems
– break them down
– make them work (better)
• Good systems analysis helps
organisations to succeed
• Necessary precursor to proper system
selection
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Requirements Analysis
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Identify elements
Model elements
Verify
Importance of Conceptual Modelling Independence from physical
implementation
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
The focus of analysis
• Systems tend to be Data-based or
Process-based (transactional)
• Transactions deal with transformations of
data, input and output
• Therefore we need to identify & develop
transactions and data, and their interaction
with the environment, to analyse a system
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
How do we do this?
• A process of expansion & contraction
– Decomposition
– Synthesis
• Identifying and relating static & dynamic
elements
– Facts
– Processes
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
The value of models
• Why do we model?
– To improve clarity and accessibility
– To show different relational aspects of the
system
– To help understanding
• Different types of model
– Data-based & Process-based
– Varieties of model
– Completeness of view
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Process modelling –
The data flow diagram
• Basic process modelling tool
– full-scale analysis involves multiple models
– different tools are used for data modelling etc
• Top-down approach
• Valuable for describing
– current physical system
– logical/desired system
• Helps us to grasp system as a whole
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Key elements and considerations
• Relationship to other models
• Components
– Sources/sinks (external entities)
– Processes
– Data stores
– Data flows
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Symbology/notation
• Importance of notation
• Data flows between
sources/sinks/stores via processes
which transform the data
• SSADM notation
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
SSADM context diagram
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
SSADM notation - first level DFD
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
SSADM notation - second level DFD
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Naming
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Importance of naming
Sources/sinks: generic descriptive
Stores: simple descriptive
Processes: “imperative action” concept
Flows: what is tranferred
Avoid ambiguity
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Hierarchies
• Concept of levelling
– Top-down decomposition
– Practical levelling
• Balancing
– Ensure all inputs and outputs balance
(match) across the levels of the hierarchy
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Referencing/numbering
• Basic principles
– Decimal heirarchies
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Lower case lettering for entities
Mn/Dn stores
Stores within processes
Single/double flow lines and direction
Multiple sources/sinks/stores
Process locations/roles (physical)
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Constructing data flow diagrams
• Follow the top-down approach
• Define boundary (context diagram)
• Identify
– Static components
– Key processes
– Flows between them
• Build -expand - refine - review
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
Refining and developing the
diagram
• Iterative process!
• Importance of
– Balancing
– Naming
– Controlling complexity
• Document flow diagrams
• Data models
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
After the break:
A brief exercise in process
modelling!
Andy Dawson
DEPARTMENT OF INFORMATION STUDIES
That’s all for today!
• Second coursework
• Any questions?
• Tomorrow:
– Wrapping up the lifecycle
– Feasibility studies and operational
requirements
– Systems selection and installation
Andy Dawson