1. Overview of 1. Overview of Software designSoftware design 1.1 Process of problem1.1 Process of problem--solving and solving and

planning for a planning for a software solution solution 1.2 After the purpose and 1.2 After the purpose and

specifications of software are specifications of software are determined, determined, software developers will will design or employ or employ designers to develop to develop a plan for a solutiona plan for a solution..

1.3 It includes low1.3 It includes low--level component level component and algorithm implementation issues and algorithm implementation issues as as well as the architectural view.well as the architectural view.

SOFTWARE DESIGN VS. LAYERSSOFTWARE DESIGN VS. LAYERS

2. Software Desin Topics:-2. Software Desin Topics:-

2.1 2.1 Design conceptsDesign concepts PProvide the rovide the software designer with a foundation from software designer with a foundation from which more sophisticated methods can bwhich more sophisticated methods can be applied. A set of fundamental design ce applied. A set of fundamental design concepts has evolved. They are:oncepts has evolved. They are:

2.1.1 2.1.1 Abstraction - - Abstraction is the Abstraction is the process or result of generalization by process or result of generalization by reducing the information content of a reducing the information content of a concept or an observable phenomenon, concept or an observable phenomenon, typically in order to retain only typically in order to retain only information which is relevant for a information which is relevant for a particular purposeparticular purpose. .

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2.1.22.1.2 Refinement - It is the process of elaboration. A hierarchy is - It is the process of elaboration. A hierarchy is developed by decomposing a macroscopic statdeveloped by decomposing a macroscopic statement of function in a stepwise fashion until prement of function in a stepwise fashion until programming language statements are reached. Iogramming language statements are reached. In each step, one or several instructions of a givn each step, one or several instructions of a given program are decomposed into more detailed en program are decomposed into more detailed instructions. instructions. Abstraction and and Refinement are complementary concepts. are complementary concepts.

2.1.3 2.1.3 Modularity - - Software architecture is divided Software architecture is divided into components called modulesinto components called modules. .

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2.1.4 2.1.4 Software Architecture - It refers to the overall - It refers to the overall structure of the software and the ways in which structure of the software and the ways in which that structure provides conceptual integrity for that structure provides conceptual integrity for a system. A software architecture is the developa system. A software architecture is the development work product that gives the highest return ment work product that gives the highest return on investment with respect to quality, schedule on investment with respect to quality, schedule and cost. and cost.

2.1.5 Control Hierarchy-2.1.5 Control Hierarchy- A program structure A program structure that represent the organization of a programthat represent the organization of a program components and implies a hierarchy of control. components and implies a hierarchy of control.

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2.1.6 Structural Partitioning2.1.6 Structural Partitioning - - The program The program structure can be divided both horizontally and structure can be divided both horizontally and vertically. Horizontal partitions define separate vertically. Horizontal partitions define separate branches of modular hierarchy for each major pbranches of modular hierarchy for each major program function. Vertical partitioning suggests trogram function. Vertical partitioning suggests that control and work should be distributed top hat control and work should be distributed top down in the program structure. down in the program structure.

2.1.7 2.1.7 Data Structure - - It is a representation of the It is a representation of the logical relationship among individual elements logical relationship among individual elements of dataof data. .

2.1.8 2.1.8 Software ProcedureSoftware Procedure - It focuses on the - It focuses on the processing of each modules individually processing of each modules individually

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2.1.9 2.1.9 Information Hiding - Modules should be specified and designed so - Modules should be specified and designed so that information contained within a module is inthat information contained within a module is inaccessible to other modules that have no need faccessible to other modules that have no need for such information. or such information.

2.2 2.2 Design considerationsDesign considerations

There are many aspects to consider in the design There are many aspects to consider in the design of a piece of software. The importance of each of a piece of software. The importance of each should reflect the goals the software is trying to should reflect the goals the software is trying to achieve. Some of these aspects are:achieve. Some of these aspects are:

Modeling languageModeling language

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2.2.1 Compatibility - The software is able to operate with other products that are designed for interoperability with another product. For example, a piece of software may be backward-compatible with an older version of itself.

2.2.2 Extensibility - New capabilities can be added to the software without major changes to the underlying architecture.

2.2.3 Fault-tolerance - The software is resistant to and able to recover from component failure.

2.2.4 Maintainability - The software can be restored to a specified condition within a specified period of time. For example, antivirus software may include the ability to periodically receive virus definition updates in order to maintain the software's effectiveness.

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2.2.5 Maintainability - The software can be restored to a specified condition within a specified period of time. For example, antivirus software may include the ability to periodically receive virus definition updates in order to maintain the software's effectiveness.

2.2.6 Modularity - the resulting software comprises well defined, independent components. That leads to better maintainability. The components could be then implemented and tested in isolation before being integrated to form a desired software system. This allows division of work in a software development project.

2.2.7 Packaging - Printed material such as the box and manuals should match the style designated for the target market and should enhance usability. All compatibility information should be visible on the outside of the package. All components required for use should be included in the package or specified as a requirement on the outside of the package.

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2.2.8 Reliability - The software is able to perform a required function under stated conditions for a specified period of time.

2.2.9 Reusability - the modular components designed should capture the essence of the functionality expected out of them and no more or less. This single-minded purpose renders the components reusable wherever there are similar needs in other designs.

2.2.10 Robustness - The software is able to operate under stress or tolerate unpredictable or invalid input. For example, it can be designed with a resilience to low memory conditions.

2.2.11 Security - The software is able to withstand hostile acts and influences.

2.2.12 Usability - The software user interface must be usable for its target user/audience. Default values for the parameters must be chosen so that they are a good choice for the majority of the users.

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2.3 2.3 A A modeling language is any artificial language that can be is any artificial language that can be used to express information or used to express information or knowledge or systems in a structure that knowledge or systems in a structure that is defined by a consistent set of rules. This defined by a consistent set of rules. The rules are used for interpretation of the e rules are used for interpretation of the meaning of components in the structure. meaning of components in the structure. A modeling language can be graphical or A modeling language can be graphical or textual. Examples of graphical modelling textual. Examples of graphical modelling languages for software design are:languages for software design are:

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2.3.1 2.3.1 Business Process Modeling Notation (BPMN) is an example of a (BPMN) is an example of a Process Modeling language. language.

2.3.22.3.2 EXPRESS and EXPRESS and EXPRESS--G G ((ISO 10303-11ISO 10303-11) ) is an is an international standard generalinternational standard general--purpose purpose data modeling languagelanguage. .

2.32.3..3 3 Extended Enterprise Modeling Language (EEML) is commonly used for business process (EEML) is commonly used for business process modeling across a number of layers. modeling across a number of layers.

2.3.4 2.3.4 Flowchart is a schematic representation of an is a schematic representation of an algorithm or a stepwise process, algorithm or a stepwise process,

2.3.5 2.3.5 Fundamental Modeling Concepts (FMC) modeling language for software-intensive (FMC) modeling language for software-intensive systems. systems.

IDEF is a family of modeling languages, the most notable of is a family of modeling languages, the most notable of which include which include IDEF0 for functional modeling, for functional modeling, IDEF1X for for information modeling, and information modeling, and IDEF5 for modeling ontologies for modeling ontologies. .

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2.3.7 2.3.7 Jackson Structured Programming (JSP) is a method for structured programming based o (JSP) is a method for structured programming based on correspondences between data stream structure and program n correspondences between data stream structure and program structure structure

2.3.8 2.3.8 LePUS3 is an is an object-oriented visual Design Description visual Design Description Language and a Language and a formal specification language that is suitable language that is suitable primarily for modelling large objectprimarily for modelling large object--oriented oriented ((Java, , C++, , C#) ) programs and programs and design patterns. .

2.3.9 2.3.9 Unified Modeling Language (UML) is a general modeling (UML) is a general modeling language to describe software both structurally and language to describe software both structurally and behaviorally. It has a graphical notation and allows for extensiobehaviorally. It has a graphical notation and allows for extension with a n with a Profile (UML). .

2.3.10 2.3.10 Alloy (specification language) is a general purpose is a general purpose specification language for expressing complex structural specification language for expressing complex structural constraints and behavior in a software systemconstraints and behavior in a software system. . It provides a It provides a concise language based on firstconcise language based on first--order relational logicorder relational logic. .

2.3.13 2.3.13 Systems Modeling Language (SysML) is a new general- (SysML) is a new general-purpose modeling language for systems engineering.purpose modeling language for systems engineering.

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2.4 2.4 Design patternsDesign patterns

A software designer or architect may A software designer or architect may identify a design problem whichidentify a design problem which has been solved by others before. has been solved by others before. A template or pattern describing a sA template or pattern describing a solution to a common problem is knolution to a common problem is known as a own as a design pattern. The reuse of such patterns can sp. The reuse of such patterns can speed up the software development preed up the software development process, having been tested and provocess, having been tested and proved in the past.ed in the past.

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2.5. 2.5. UsageUsage

Software Software design documentation may be reviewed or presented to allow may be reviewed or presented to allow constraints, specifications and even constraints, specifications and even requirements to be adjusted prior to requirements to be adjusted prior to programming. Redesign may occur after review of a program. Redesign may occur after review of a programmed med simulation or or prototype. It is possible to design software in the process . It is possible to design software in the process of programming, without a plan or requirement of programming, without a plan or requirement analysis, but for more complex projects this woanalysis, but for more complex projects this would not be considered a professional approach. uld not be considered a professional approach.

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3. 3. COMMON LAYERS COMMON LAYERS ภายใต้ระบบสารสนเทศ ภายใต้ระบบสารสนเทศ ((ของของระบบธรรมชาติสิง่แวดล้อมระบบธรรมชาติสิง่แวดล้อม) ) ท่ีมกีารออกแบบท่ีมกีารออกแบบสถาปัตยกรรมเชงิตรรก สถาปัตยกรรมเชงิตรรก 4 4 ชัน่ชัน่ (in an IS Logical (in an IS Logical Architecture 4 LAYERS) :-Architecture 4 LAYERS) :-

The following four layers are the most The following four layers are the most

common common layers in a logical in a logical multilayered architecturemultilayered architecture for an for an information system with an information system with an objectobject--oriented designoriented design::

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1.1. User Interface Layer:- User Interface Layer:-

• aka View Layeraka View Layer

• UI layer UI layer

• Presentation layerPresentation layer

2.2. Application LayerApplication Layer

• aka Service Layeraka Service Layer

• GRASPGRASP

• Controller LayerController Layer

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3.3. Domain LayerDomain Layer

• aka Business Layeraka Business Layer

• Business logic LayerBusiness logic Layer

• Model LayerModel Layer

4. Infrastructure Layer

• data access or other persistence, logging, network I/O e.g. sending emails, and other kind of technical services

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