system development tools, techniques and methods
DESCRIPTION
System Development Tools, Techniques and Methods . Structured Process Modelling. What we will cover. Process Modelling in principle Data Flow Diagrams in principle Symbols and Semantics Process Modelling in action Data Flow diagrams in practice Other process modelling techniques . - PowerPoint PPT PresentationTRANSCRIPT
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System Development Tools, Techniques and Methods
Structured Process Modelling
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What we will cover
Process Modelling in principle Data Flow Diagrams in principle Symbols and Semantics Process Modelling in action Data Flow diagrams in practice Other process modelling techniques
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Context Diagrams and DFDs
Symbols System (for context only) External entity Data Flow Process Data Store System boundary (Material Flow)
Definitions in a moment
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When process models are used Current physical
the how of now Current logical
the what of now Proposed logical
the what of the new Proposed physical
the how of the new
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Current physical process model
two volunteers please one student one bar steward
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External Entity
Person, organisation or system outside the system being considered
Communicates only with system process via data flows
Student
Serve bottle of Bud
1 Bar stewardRequest for bottle of Bud
Student
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Data Flow
The direction of flow of data from source to recipient Always has a description
Serve bottle of Bud
1 Bar stewardRequest for bottle of Bud
Student
Request for bottle of Bud
Key element in determining data needed by and in system
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Process
where something happens to data (transformed, validated, stored …)
always has a number always has a description (strong verb, strong
noun, maybe qualifier) always has a location/executor
1 Bar steward
Serve bottle of Bud
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Data Store
a location where data is stored may be manual or computer (M or D) always has a number and descriptor
Till M1
Serve bottle of Bud
1 Bar Steward
Till M1
Money offered
Change notification
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Material Flow
A newish, non-purist representation of the movement of material
Student Serve bottle of Bud
1 Bar stewardBottle of Bud
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System (context only)
Represents the system as a whole may include non-computer functions shows no detail of internal processes or
data stores used only for context diagrams
UCAS Admissions System
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Oversimple context diagram
BACS
Money and account details
Employee
Timesheet
Personal and account details
Money
Tax rules
NI rules
Other legal stuff
Statutory bodies
Payroll System
Payslip
Statutory payments and account details
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Another Context Diagram
Customer
Video HireSystem
Membership Application Request
Membership Details
Returned Video
Fee
Hire Video
Membership Application Response
Membership card
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Levelling
Top Level - Context diagram (also known as Level 0 DFD)
Next level - Level 1 DFD Next level - Level 2 DFD and so on you are unlikely to need more than 3! Numbering of lower level processes links
processes between levels
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Levelling - Graphically
Context
Level 1
Level 2
L
e
v
e
l
3
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Textual descriptions
Every symbol represented on a process model should have a more detailed textual description linked to it
Can be achieved in CASE tool Can be achieved with other, linked text (which
is what you will do for your assignment) Provides explanatory detail
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Example of levelling
Level 0 Video Hire System
Level 1 Process 1 Administer Membership
Level 2 Process 1.1 Receive membership
application
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Data dictionary A precise and unambiguous way of storing data
about the data identified in data flows and data stores on DFDs
Links DFDs and ERMs (you will understand more about this before
Christmas) Provides the basis for ER Modelling Needed for SAD assignment 2 – see Britton and
Doake’s Structure Analysis book, Chapter 4
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Problem/Requirements list A numbered list of all the problems with the current
system and (usually hence) requirements of a new system
Does not differentiate between whether issue is a problem or a requirement
Serves as a check-list when conceiving and designing new system
Helps to prevent problems and requirements becoming lost in the depths of analysis and design methods
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Things we haven’t covered
rules for building models “sensibleness” checks for DFDs
Britton and Doake Chapter 4 detail of textual descriptions
Tutorials, self guided study, Valachi, George and Hoffer and assignment
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Health warning
Process modelling only makes sense when you do it (it seems trivial otherwise)