Unit 3 Software engineering deataled notes .docx
- 2. Topics to be covered... Concept of Software Design Architectural and Procedural Design Modularization Design Structure Charts Pseudo Codes Coupling and Cohesion Measures Function Oriented Design Object Oriented Design Top-Down and Bottom-Up Design Measurement and Metrics Halestead’s Software Science Function Point (FP) Based Measures Cyclomatic Complexity Measures Happy Ending!
- 4. Concept of Software Design Software design is a mechanism to transform user requirements into some suitable form, which helps the programmer in software coding and implementation. It allows the software engineer to create the model of the software that is to be developed. The software design phase is the first step in SDLC (Software Design Life Cycle), which moves the concentration from the problem domain to the solution domain. General task involved in design process: 1.Design the overall the system processes. 2.Segmenting the system into smaller modules. 3. Designing the database structure. 4. Documenting the system design.
- 5. Concept of Software Design Objectives: 1.Correctness: Software design should be correct as per requirement. It should correctly implement all the functionalities of the system. 2.Completeness: The design should have all components like data structures, modules, and external interfaces, etc. 3.Efficiency: Resources should be used efficiently by the program. 4. Flexibility: Able to modify on changing needs. 5.Consistency: There should not be any inconsistency in the design. 6.Maintainability: The design should be so simple so that it can be easily maintainable by other designers. Concepts of Software Design: The software design concept simply means the idea or principle behind the design. It describes how you plan to solve the problem of designing software, the logic, or thinking behind how you will design software. It allows the software engineer to create the model of the system or software or product that is to be developed or built.
- 7. Architectural Design The process of defining a collection of hardware and software components and their interfaces to establish the framework for the development of a computer system. The output of this design process is a description of the software architecture. Architectural design is an early stage of the system design process. It represents the link between specification and design processes and is often carried out in parallel with some specification activities. A set of components(eg: a database, computational modules) that will perform a function required by the system. The set of connectors will help in coordination, communication, and cooperation between the components.
- 8. Conditions that how components can be integrated to form the system.
- 9. Architectural Design Data Centered Architecture: Data Centered Architecture is a layered process which provides architectural guidelines in data center development. Data Centered Architecture is also known as Database Centric Architecture. This architecture is the physical and logical layout of the resources and equipment within a data center facility.
- 10. Architectural Design Data flow architectures: This kind of architecture is used when input data to be transformed into output data through a series of computational manipulative components. The figure represents pipe-and-filter architecture since it uses both pipe and filter and it has a set of components called filters connected by pipes. Pipes are used to transmit data from one component to the next.
- 12. Procedural Design Procedural design used to model programs that have an obvious flow of data from input to output. It represents the architecture of a program as a set of interacting processes that pass data from one to another. Procedural design is also called components design. It is completely based on process and control specification. The "state transition diagram" of the requirement analysis model is also used in components design. Components design is usually done after user interface design.
- 13. Modularization
- 14. Modularization Modularity in design refers to the splitting of a large software system into smaller connected modules. Modules are interconnected through their interfaces. The interconnection should be simple to avoid costly maintenance. Two modules are directly connected if one module can call the other module. Modularity has several key benefits: Testing & Debugging Since each component is self-contained, you mitigate dependency issues. It becomes easy to test each component in isolation by using a mocking or isolation framework. Reusability If you discover you need the same functionality in a new project, you can package the existing functionality into something reusable by multiple projects without copying and pasting the code. Extensibility Your software now runs as a set of independent components connected by an abstraction layer.
- 15. Advantage of modularization Smaller components are easier to maintain Program can be divided based on functional aspects Easier because programmer only focus on one small simple problem rather than a large complex problem. Testing and Debugging easier. Easy to isolate bugs and easy to fix bugs.
- 17. Design Structure Charts A Structure Chart (SC) in software engineering and organizational theory is a chart which shows the breakdown of a system to its lowest manageable levels. They are used in structured programming to arrange program modules into a tree. Each module is represented by a box, which contains the module's name. The tree shows the relationship between modules, showing data transfer between the models. Data being passed from module to module that needs to be processed. Structure chart is a chart derived from a Data Flow Diagram. It represents the system in more detail than DFD. It breaks down the entire system into lowest functional modules, describes functions and sub-functions of each module of the system to a greater detail than DFD.
- 20. Pseudo Codes
- 21. Pseudo Codes Pseudo code uses the vocabulary of one language i.e, English and syntax of another i.e, any structured programming language. Pseudo code is a combination of algorithm written in a simple language and programming language statements. Using Pseudo code, the designer design describes system characteristics structured by keywords such as IF-THEN-ELSE, while-do and end.
- 22. Advantages of Pseudo Codes Converting a Pseudo code to a programming language is much easier as compared to converting to flowchart or decision table. It is easier to modify whenever programmer modification are necessary. Take less time to writing as compared to drawing flow chart. Done easily on Word Processor
- 24. Coupling The coupling is the degree of interdependence between software modules. Two modules that are tightly coupled are strongly dependent on each other. However, two modules that are loosely coupled are not dependent on each other. Uncoupled modules have no interdependence at all within them. A good design is the one that has low coupling. Coupling is measured by the number of relations between the modules. That is, the coupling increases as the number of calls between modules increase. Thus, it can be said that a design with high coupling will have more errors.
- 25. Coupling Types of Module Coupling:
- 26. Coupling Data Coupling: When data of one module is passed to another module, this is called data coupling. Stamp Coupling: Two modules are stamp coupled if they communicate using composite data items such as structure, objects, etc. When the module passes entire structure to another module, they are said to be stamp coupled. For example, passing structure variable in C or object in C++ language to a module.
- 27. Coupling Control Coupling: Control Coupling exists among two modules if data from one module is used to direct the structure of instruction execution in another. External Coupling: External Coupling arises when two modules share an externally imposed data format, communication protocols, or device interface. This is related to communication to external tools and devices. Common Coupling: Two modules are common coupled if they share information through some global data items.
- 28. Cohesion Cohesion shows the relationship within the module. Cohesion is an ordinal type of measurement and is generally described as "high cohesion" or "low cohesion."
- 30. Cohesion 1.Functional Cohesion: Functional Cohesion is said to exist if the different elements of a module, cooperate to achieve a single function. 2.Sequential Cohesion: If the element of a module form the components of the sequence, where the output from one component of the sequence is input to the next. 3.Communicational Cohesion: If all tasks of the module refer to or update the same data structure, e.g., the set of functions defined on an array or a stack. 4.Procedural Cohesion: If the set of purpose of the module are all parts of a procedure in which particular sequence of steps has to be carried out for achieving a goal, e.g., the algorithm for decoding a message. 5.Temporal Cohesion: When a module includes functions that are associated by the fact that all the methods must be executed in the same time. 6.Logical Cohesion: If all the elements of the module perform a similar operation. For example Error handling, data input and data output, etc. 7.Coincidental Cohesion: If it performs a set of tasks that are associated with each other very loosely, if at all.
- 31. Coupling Cohesion Coupling is also called Inter-Module Binding. Coupling shows the relationships between modules. In coupling, modules are linked to the other modules. Cohesion is also called Intra-Module Binding. Cohesion shows the relationship within the module. In cohesion, the module focuses on a single thing.
- 33. Function Oriented Design Function Oriented Design is an approach to software design where the design is decomposed into a set of interacting units where each unit has a clearly defined function.
- 34. Function Oriented Design Techniques used by Function Oriented Design are: Data Flow Diagram(A data flow diagram (DFD) maps out the flow of information for any process or system. ) Data Dictionaries(Data dictionaries are simply repositories to store information about all data items defined in DFDs. At the requirement stage, data dictionaries contain data items.) Structure Charts(Components are read from top to bottom and left to right. When a module calls another, it views the called module as black box, passing required parameters and receiving results) Pseudo Codes(It uses keywords and indentation. Pseudo codes are used as replacement for flow charts. It decreases the amount of documentation required.)
- 37. Object Oriented Design Object-oriented design is the process of planning a system of interacting objects for the purpose of solving a software problem. It is one approach to software design. In the object-oriented design method, the system is viewed as a collection of objects (i.e., entities).
- 39. Top-Down and Bottom-Up Design
- 41. Measurement A software metric is a measure of software characteristics which are measurable or countable. Software metrics are valuable for many reasons, including measuring software performance, planning work items, measuring productivity, and many other uses. Within the software development process, many metrics are that are all connected. Software metrics are similar to the four functions of management: Planning, Organization, Control, or Improvement. Need of Software Measurement: Software is measured to: Create the quality of the current product or process. Anticipate future qualities of the product or process. Enhance the quality of a product or process. Regulate the state of the project in relation to budget and schedule.
- 42. Metrics A metric is a measurement of the level that any impute belongs to a system product or process. There are 4 functions related to software metrics: 1. Planning 2. Organizing 3. Controlling 4. Improving
- 44. Metrics Classification of Software Metrics: There are 3 types of software metrics: Product Metrics: Product metrics are used to evaluate the state of the product, tracing risks and undercovering prospective problem areas. The ability of team to control quality is evaluated. Process Metrics: Process metrics pay particular attention on enhancing the long term process of the team or organization. Project Metrics: The project matrix describes the project characteristic and execution process. Number of software developer Staffing pattern over the life cycle of software Cost and schedule
- 45. Productivity
- 48. Measurement Advantages: Predicts error rate. Predicts maintenance effort Simple to calculate Measure overall quality Used for any language Disadvantages: Depends on complete code Complexity increases as program level decreases Difficult to compute
- 49. Function Point (FP) Based Measures
- 50. Function Point (FP) Based Measures Function point is used in the estimation of software development cost which is the most important potential use of function point data. Function point may be used to compute the following importance metrics: Productivity = FP/persons-months Quality = Defects/FP Cost = Rupees/FP Organizations that use function point method develop criteria for determining whether a particular entry is low, average or high.
- 51. Function Point (FP) Based Measures There are three types of transaction functions. External Inputs External Outputs External Inquiries Advantages: Size oriented metrics Language dependent Understood by the non technical user To estimate cost and resources required for software development Disadvantages: Manually Counting Process Difficult to Understand Requires Experience
- 52. Function Point (FP) Based Measures
- 54. Cyclomatic Complexity Measures Cyclomatic complexity is a software metric used to measure the complexity of a program. It gives the quantitative measure of logical complexity of the program. How to Calculate Cyclomatic Complexity? McCabe proposed the cyclomatic number, V (G) of graph theory as an indicator of software complexity. The cyclomatic number is equal to the number of linearly independent paths through a program in its graphs representation. For a program control graph G, cyclomatic number, V (G), is given as: V (G) = E - N + 2 * P E = The number of edges in graphs G N = The number of nodes in graphs G P = The number of connected components in graph G.
- 56. Cyclomatic Complexity Measures Advantages: Gives complexity of various designs Computed early in life cycle Easy to apply Measures minimum effort Disadvantages: Measures program’s control complexity and not the data complexity Nested conditional structures are harder to understand Ignore the size of the program