System Analysis & design

Transcription

1 Assiut University Faculty of Computers and Information System Analysis & design Year 2 Academic Year 2014/ 2015 Term (2) Copyright 2014 Dr. Hossam Ragab

2 8 A n important component of the design phase is the architecture design, which describes the system s hardware, software, and network environment. The architecture design flows primarily from the nonfunctional requirements, such as operational, performance, security, cultural, and political requirements. The deliverables from architecture design include the architecture design and the hardware and software specification.

3 OBJECTIVES Describe the fundamental components of an information system. Describe server-based, client-based, and client server architectures. Describe newer architectural options, such as cloud computing. Explain how operational, performance, security, cultural, and political requirements affect the architecture design. Create an architectural design. Create a hardware and software specification.

4 ARCHITECTURE DESIGN An important step of the design phase is the creation of the architecture design, the plan for how the information system components will be distributed across multiple computers and what hardware, operating system software, and application software will be used on each computer (e.g., Windows or Linux operating system software). The nonfunctional requirements developed early in the analysis phase play a key role in architecture design. These requirements are reexamined and refined into more detailed requirements that influence the system s architecture. The objective of architecture design is to determine how the software components of the information system will be assigned to the hardware devices of the system.

5 ELEMENTS OF AN ARCHITECTURE DESIGN Architectural Components The major architectural components of any system are the software and the hardware. The major software components of the system being developed have to be identified and then allocated to the various hardware components on which the system will operate. Software systems can be divided into four basic functions, which are the basic building blocks of any information system. 1. Data storage; Most information systems require data to be stored and retrieved, whether a small file or a large database. These are the data entities documented in ERDs. 2. Data access logic; the processing required to access data, often meaning database queries in Structured Query Language (SQL) 3. Application logic; the logic documented in the DFDs, use cases, and functional requirements. 4. Presentation logic; the display of information to the user and the acceptance of the user s commands (the user interface)

6 ELEMENTS OF AN ARCHITECTURE DESIGN Architectural Components Hardware components of a systems are client computers, servers, and the network that connects them. 1. Client computers; are the input output devices employed by the user and are usually descktop or laptop computers, and also handheld devices, smartphones, special-purpose terminals. 2. Servers; are larger multi-user computers used to store software and data. 3. The network that connects the computers can vary in speed from slow, to medium-speed, to fast, to high-speed.

7 ELEMENTS OF AN ARCHITECTURE DESIGN Client Server Architectures attempt to balance the processing between client devices and one or more server devices. The client is responsible for the presentation logic, The server is responsible for the data access logic and data storage. The application logic may reside on the client, reside on the server, or be split between both Two-Tiered Client Server Architecture ** If the client contained all or most of the application logic, it is called a thick or fat client

8 ELEMENTS OF AN ARCHITECTURE DESIGN Client Server Architectures have four important benefits; They are scalable, that means it is easy to increase or decrease the storage and processing capabilities of the servers. can support many different types of clients and servers. It is possible to connect computers that use different operating systems so that you are not locked into one vendor. (Middleware is a type of system software designed to translate between different vendors software, and installed on both the client and server computers) for thin client server architectures that use Internet standards, it is simple to clearly separate the presentation logic, the application logic, and the data access logic and design each to be somewhat independent. it is possible to change the application logic without changing the presentation logic or the data, which are stored in databases if a server fails in a client server architecture, only the applications requiring that server will fail. The failed server can be swapped out and replaced and the applications can then be restored Client server architectures have critical limitations; The complexity of writing the software and / or updating the overall system, due to all applications in client server computing have two parts, the software on the client side and the software on the server side.

9 ELEMENTS OF AN ARCHITECTURE DESIGN Client Server Tiers; There are many ways in which the application logic can be partitioned between the client and the server. In the Two-Tiered Client Server Architecture the server is responsible for the data and the client is responsible for the application and presentation, and it called a two-tiered architecture because it uses only two sets of computers clients and servers A three-tiered architecture uses three sets of computers, the software on the client computer is responsible for presentation logic, an application server(s) is responsible for the application logic, and a separate database server(s) is responsible for the data access logic and data storage

10 An n-tiered architecture distributes the work of the application (the middle tier) among multiple layers of more specialized server computers. This type of architecture is common in today s Web-based e-commerce systems. The browser software on client computers makes HTTP requests to view pages from the Web server(s), and the Web server(s) enable the user to view merchandise for sale by responding with HTML documents As the user shops, components on the application server(s) are called as needed to allow the user to put items in a shopping cart; determine item pricing and availability; compute purchase costs, sales tax, and shipping costs; authorize payments, etc.., those elements of business logic, or detailed processing, are stored on the application server(s) and are accessible to any application. The database server(s) manage the data components of the system. Each of these four components is separate, which makes it easy to spread the different components on different servers and to partition the application logic on a Web-oriented server and a business-oriented server.

11 n-tiered architecture advantage compared with two / three - tiered architecture is that; it separates out the processing that occurs to better balance the load on the different servers; it is more scalable If we discover that the application server is too heavily loaded, we can simply replace it with a more powerful server or just put in several more application servers to share the load. if we discover that the database server is underused, we could store data from another application on it. n-tiered architecture disadvantage compared with two/three - tiered architecture are that; the configuration puts a greater load on the network the n-tiered model requires more communication among the servers; it generates more network traffic, so you need a higher-capacity network it is much more difficult to program and test software in n-tiered architectures than in two-tiered architectures, because more devices have to communicate properly to complete a user s transaction

12 Less Common Architectures Server-Based Architectures The very first computing architectures were serverbased, with the server (usually, a central mainframe computer) performing all four application functions. The clients (usually, terminals) enabled users to send and receive messages to and from the server computer. The clients merely captured keystrokes and sent them to the server for processing, and accepted instructions from the server on what to display This very simple architecture often works very well. Application software is developed and stored on the server, and all data are on the same computer. There is one point of control because all messages flow through the one central server. Software development and software administration are simplified because a single computer hosts the entire system (operating system and application software).

13 Less Common Architectures Client-Based Architectures With client-based architectures, the clients are microcomputers on a local area network, and the server is a server computer on the same network. The application software on the client computers is responsible for the presentation logic, the application logic, and the data access logic; the server simply provides storage for the data This simple architecture often works very well in situations with low numbers of users or limited data access requirements. The fundamental problem in the clientbased architecture is that all data on the server must travel to the client for processing.

14 Advances in Architecture Configurations Advances in hardware, software, and networking have given rise to a number of new architecture options. Two advances that are currently getting a lot of attention, virtualization and cloud computing. Virtualization This term, in the computing domain, refers to the creation of a virtual device or resource, such as a server or storage device. Server virtualization involves partitioning a physical server into smaller virtual servers. Software is used to divide the physical server into multiple virtual environments, called virtual or private servers. Storage virtualization involves combining multiple network storage devices into what appears to be single storage unit. Storage area network (SAN) uses storage virtualization to create a highspeed sub network of shared storage devices In this environment, tasks such as backup, archiving, and recovery are easier and faster.

15 Advances in Architecture Configurations Cloud computing This term refers to everything, from computing power to computing infrastructure, applications, business processes to personal collaboration of which can be delivered as a service wherever and whenever needed, It is no longer necessary for organizations to own, manage, and administer their own computing infrastructure. Cloud computing can be defined as the set of hardware, networks, storage, services, and interfaces that combine to deliver aspects of computing as a service, and it can be implemented in three ways: private cloud, public cloud, and hybrid clouds. Public clouds, services are provided as a service over the Internet with little or no control over the underlying technology infrastructure Private clouds offer activities and functions as a service, but are deployed over a company intranet or hosted data center Hybrid clouds combine the power of both public and private clouds, activities and tasks are allocated to private or public clouds as required Cloud computing suppliers utilize virtualization as a key enabling technology, for cloud computing customers, the point is to outsource IT technology, applications, and skills with a pay per usage model. Through the cloud computing model, the power of virtualization is converted into measurable business value.

16 CREATING AN ARCHITECTURE DESIGN The architecture design specifies the overall architecture and the placement of software and hardware that will be used. Creating an architecture design begins with the nonfunctional requirements. The first step is to refine the nonfunctional requirements into more detailed requirements Then employed those detailed nonfunctional requirements to help select the architecture to be used (server-based, client-based, or client server) and the software components to be placed on each device. In a client server architecture, it has to decide whether to use a two-tier, three-tier, or n-tier architecture. There are four primary types of nonfunctional requirements that can be important in designing the architecture: 1. Operational requirements, 2. Performance requirements, 3. Security requirements, and 4. Cultural and political requirements.

17 CREATING AN ARCHITECTURE DESIGN Operational requirements, specify the operating environment in which the system must perform and how those may change over time. (operating systems, system software, and information systems with which the system must interact, but will on occasion also include the physical environment if the environment is important to the application e.g., in a noisy factory floor where no audible alerts can be heard). The four key operational requirement areas are; 1. Technical Environment Requirements Specify the type of hardware and software on which the system will work, usually focus on the operating system software (e.g., Windows, Linux), database system software (e.g., Oracle), and other system software (e.g., Internet Explorer). 2. System Integration Requirements need to the system to operate with other information systems, either inside or outside the company. These typically specify interfaces through which data will be exchanged with other systems. 3. Portability Requirements define how the technical operating environments may evolve over time and how the system must respond (e.g., the system may currently run on Windows Vista, but in the future may have to run on Windows 7 and Linux). Portability requirements also refer to potential changes in business requirements that will drive technical-environment changes. For example, many organizations today are working to ensure their applications are optimized for devices such as the ipad in response to user demand. 4. Maintainability Requirements specify the business requirement changes that can be anticipated, not all changes are predictable but some are.

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19 CREATING AN ARCHITECTURE DESIGN Performance Requirements, focus on performance issues such as response time, capacity, and reliability. As analysts define the performance requirements for the system, the testability of those requirements is a key issue. Each requirement must be measurable so that a benchmark comparison can be made. The three key Performance requirement areas are; 1. Speed Requirements (a) how fast the system must operate (the response time of the system), and (b) how long it takes transactions in one part of the system to be reflected in other parts. 2. Capacity Requirements attempt to predict how many users the system will have to support, both in total and simultaneously. 3. Availability and Reliability Requirements focus on the extent to which users can assume that the system will be available for them to use. While some systems are intended to be used just during the 40-hour work week, other systems are designed to be used by people around the world

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21 CREATING AN ARCHITECTURE DESIGN Security Requirements, Security is the ability to protect the information system from disruption and data loss, whether caused by an intentional act (e.g., a hacker or a terrorist attack) or a random event (e.g., disk failure, tornado). Security is primarily the responsibility of the operations group, the staff responsible for installing and operating security controls such as firewalls, intrusion detection systems, and routine backup and recovery operations. Developers of new systems must ensure that the system s security requirements produce reasonable precautions to prevent problems; system developers are responsible for ensuring security within the information systems themselves. System developers must know the security standards that are applicable to their organizations. The most important computer asset in any organization is not the equipment; it is the organization s data. Security within systems usually focuses on; 1. specifying who can access what data, 2. identifying the need for encryption and authentication, and 3. ensuring that the application prevents the spread of viruses.

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23 CREATING AN ARCHITECTURE DESIGN Cultural and Political Requirements, are specific to the countries in which the system will be used. Important part of the design of the system s architecture is understanding the global cultural and political requirements for the system

24 CREATING AN ARCHITECTURE DESIGN Designing the Architecture Operational Requirements System integration requirements may lead to one architecture over another, depending upon the architecture and design of the system(s) with which the system needs to integrate Performance Requirements information systems that have high performance requirements are best suited to client server architectures. Security Requirements, server-based architectures tend to be more secure because all software is in one location and because mainframe operating systems are more secure than microcomputer operating systems. Cultural and Political Requirements As the cultural and political requirements become more important, the ability to separate the presentation logic from the application logic and the data becomes important. Nonfunctional Requirements and Their Implications for Architecture Design

25 HARDWARE AND SOFTWARE SPECIFICATION The hardware and software specification is a document that describes what hardware and software are needed to support the application. When a specification document is created, the hardware needed to support the future system is listed and then described in as much detail as possible. Next, the software to run on each hardware component is written down, along with any additional associated costs, such as technical training, maintenance, extended warranties, and licensing agreements. The project team will work in conjunction with the purchasing department to acquire the hardware and software.

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