1. COMP6015 An Introduction to Computer Programming
Lecture 08
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2. Software Engineering Customer sees an Opportunity!!!
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3. Software Engineering How the customer explained it!
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4. Software Engineering How the project leader understood it!!!
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5. Software Engineering How the analyst designed it!!!
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6. Software Engineering How the programmer coded it!!!
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7. Software Engineering How Marketing described it!!!
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8. Software Engineering How the project was documented!!!
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9. Software Engineering What operations installed!!!
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10. Software Engineering What the customer was billed!!!
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11. Software Engineering How it was supported!!!
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12. Software Engineering What the customer actually wanted!!!
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13. Software specification Software design and implementation
Software Engineering
A structured set of activities required to develop a software system.
Activities include:
Software specification
Software design and implementation
Software integration and validation
Software maintenance and evolution
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14. Software Engineering Software specification:
The process of establishing what services are required and the constraints on the system’s operation and development.
Requirements engineering process
Feasibility study;
Requirements elicitation and analysis;
Requirements specification;
Requirements validation.
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15. Software Engineering Software specification: Specification documents
Must be:
Clear
Complete
Correct
Understood by both the client as well as the future design teams.
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16. Software Engineering Software specification: Specification documents
Must also clearly outline the constraints of the proposed system including:
Restrictions on hardware
Portability
Reliability
Timing
other resource usage issues. 
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17. Software Engineering Software specification: Specification documents
Can be expressed:
Informally
Semi-formally
Formally
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18. Software Engineering Software specification: Specification documents
Informal Specification
Takes the form of natural language to express the specifications in statements such as:
"If the total revenue generated from sales for the previous quarter are higher then the total sales from the current quarter then raise prices by 0.5%"
Despite best attempts at grammatical and linguistic exactitude, informal specifications tend to be ambiguous, incomplete and imprecise. Nevertheless this method is still very popular and potential misunderstandings may be caught by working closely with the client.
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19. Software Engineering Software specification: Specification documents
Semi-formal Specification
A variety of semi-formal techniques exist for writing specifications, including :-
Data Flow Diagrams (DFDs)
Entity-Relationship Modeling
A Data Flow Diagram is a pictorial representation of all aspects of the logical data flows.
DFDs are developed using stepwise refinement techniques and will go through a set of revisions/clarifications while they are being developed.
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20. Semi-formal Specification
Software Engineering
Software specification: Specification documents
Semi-formal Specification
Entity-Relationship Modeling
Technique used to specify databases, relations and processes.
ERMs allow a range from very simple to very complex relationships to be expressed.
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21. Software Engineering Formal Specification
Software specification: Specification documents
Formal Specification
This includes the use of finite state machines, Petri nets, formal specifications language languages.
Formal techniques require a higher level of mathematical rigor than semi-formal techniques.
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22. Software Engineering Software specification: Pros & Cons of Techniques
Informal techniques are relatively easy to learn but does not have the power, expressiveness and clarity of semi-formal or formal techniques.
Formal techniques are powerful but are hard to learn and use. The client may have difficulty in understanding formal specifications.
Many times circumstances will dictate the technique that is used. If no one is familiar with formal techniques then an informal or semi-formal approach will have to be taken.
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23. Software Engineering Software design and implementation
Software design is a meaningful engineering representation of some software product that is to be built.
Design should be traced to the customer's requirements and could be assessed for quality against predefined criteria.
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24. Software Engineering Software design and implementation
In the software engineering context, design focuses on four major areas of concern:
Data
Architecture
Interfaces
Components.
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25. Data Software Engineering Software design and implementation
Created by transforming the analysis information model (data dictionary and ERD) into data structures required to implement the software.
Part of the data design may occur in conjunction with the design of software architecture.
More detailed data design occurs as each software component is designed.
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26. Software Engineering Architecture Software design and implementation
Defines the relationships among the major structural elements of the software, the “design patterns” and can be used to achieve the requirements that have been defined for the system, and the constraints that affect the way in which the architectural patterns can be applied.
It is derived from the system specification, the analysis model, and the subsystem interactions defined in the analysis model (DFD).
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27. Interfaces Software Engineering Software design and implementation
Describes how the software elements communicate with each other, with other systems, and with human users.
The data flow and control flow diagrams provide much of the necessary information required.
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28. Software Engineering Components Software design and implementation
Created by transforming the structural elements defined by the software architecture into procedural descriptions of software components using information obtained from the process specification (PSPEC), control specification (CSPEC), and state transition diagram (STD).
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29. Software Engineering Software design and implementation
The fundamental design concepts are:
Abstraction - focus on solving a problem without being concerned with lower level details.
Refinement - provides successively more detail for each design component.
Modularity – understanding components independently of one another.
Software architecture - structure and conceptual integrity of the software components.
Control hierarchy or program structure - module organization (control hierarchy; not concerned with procedural aspects of software).
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30. Software Engineering Software design and implementation
The fundamental design concepts are:
Structural partitioning – (Horizontal) define input, data transformations, and output); (vertical) top-down refinement
Data structure - logical relationship among individual data elements
Software procedure - precise specification of processing (event sequences, decision points, repetitive operations, data organization/structure)
Information hiding – Modules’ need-to-know basis
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31. Software Engineering Implementation Software design and implementation
The process of translating the detailed design into code.
Generally done by teams all working at the same time on different components of the product.
Major documentation provided in this stage is the source code; however, the programmer should provide additional documentation to assist in maintenance. This additional documentation includes all test cases against which the code should be tested, the expected results, and the actual output. These documents will be used in regression testing.
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32. Software Engineering
Software design and implementation: Implementation
Issues involved:
Choice of programming language
In many cases, there is no opportunity for choice because either only one choice is available or management stipulates that the product should be implemented in a given language.
A cost-benefit analysis may be employed to decide on the language. The language with the largest expected gain would be the one selected.
A risk analysis may also be used to aid in the selection of the language. The language with the smallest overall risk is selected.
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33. Software Engineering Issues involved:
Software design and implementation: Implementation
Issues involved:
The use of 4th generation languages (4GLs)
The ease of programming
The program is shorter, quicker to develop and easier to maintain
There is a potential productivity gain
4GLs such as FoxPro and PowerHouse have case tool features (e.g. automatic documentation) which aid in the implementation process.
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34. Software Engineering Issues involved:
Software design and implementation: Implementation
Issues involved:
Use of good programming practices
use of consistent and meaningful variable names
provision of proper documentation; both prologue and inline comments
use of parameters (as opposed to constants)
well formatted source code to increase readability; good use of blanks and indentation to highlight control structures.
Structured programming (i.e. modular programming) is also advised to improve code quality, maintainability and decrease the effort required for testing.
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35. Waterfall Model Software Engineering Software Development
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36. Software Engineering Waterfall Model Advantages
Testing is inherent to every phase of the waterfall model
It is an enforced disciplined approach
It is documentation driven, that is, documentation is produced at every stage
Disadvantages
Changes may cause considerable confusion as the project progresses. 
As The client usually only has a vague idea of exactly what is required from the software product, this WM has difficulty accommodating the natural uncertainty that exists at the beginning of the project.
The customer only sees a working version of the product after it has been coded. This may result in disaster if any undetected problems are precipitated to this stage.
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37. Incremental Model Software Engineering Software Development
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38. Software Engineering Incremental Model
Model combines the elements of the waterfall model with the iterative philosophy of prototyping. However, unlike prototyping the IM focuses on the delivery of an operational product at the end of each increment.
Example of incremental approach:
Develop a Word Processor
1.  Basic file management, editing and document production functions.
2. Advanced editing and document production functions
3. Spell and grammar checking
4. Advance page layout
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