Continuation of Systems and Designs, Assignments of Design and Analysis of Algorithms

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SYSTEM DESIGN

System design is the phase that bridges the gap between problem domain and the existing system in a manageable way. This phase focuses on the solution domain, i.e. “how to implement?”

It is the phase where the SRS (System Requirement Specification) document is converted into a format that can be implemented and decides how the system will operate.

In this phase, the complex activity of system development is divided into several smaller sub-activities, which coordinate with each other to achieve the main objective of system development.

Inputs to System Design System design takes the following inputs: Statement of work Requirement determination plan Current situation analysis

Proposed system requirements including a conceptual data model, modified DFDs, and Metadata (data about data).

Outputs for System Design System design gives the following outputs: Infrastructure and organizational changes for the proposed system. A data schema, often a relational schema. Metadata to define the tables/files and columns/data-items. A function hierarchy diagram or web page map that graphically describes the program structure. Actual or pseudocode for each module in the program. A prototype for the proposed system.

Types of System Design Logical Design Logical design pertains to an abstract representation of the data flow, inputs, and outputs of the system. It describes the inputs (sources), outputs (destinations), databases (data stores), procedures (data flows) all in a format that meets the user requirements.

While preparing the logical design of a system, the system analyst specifies the user needs at level of detail that virtually determines the information flow into and out of the system and the required data sources. Data flow diagram, E-R diagram modeling are used.

Physical Design Physical design relates to the actual input and output processes of the system. It focuses on how data is entered into a system, verified, processed, and displayed as output.

Entity Relationship Model It is a technique used in database design that helps describe the relationship between various entities of an organization.

Terms used in E-R model Symbols used in E-R model and their respective meanings ENTITY: It specifies distinct real world items in an application. For example: vendor, item, student, course, teachers, etc. RELATIONSHIP: They are the meaningful dependencies between entities. For example, vendor supplies items, teacher teaches courses, then supplies and course are relationship. ATTRIBUTES: It specifies the properties of relationships. For example, vendor code, student name. The following table shows the symbols used in E-R model and their significance:

Three types of relationships can exist between two sets of data: one-to-one, one-to-many, and many-to-many.

File Organization It describes how records are stored within a file. There are four file organization methods: Serial: Records are stored in chronological order (in order as they are input or occur). Examples: Recording of telephone charges, ATM transactions, Telephone queues Sequential: Records are stored in order based on a key field which contains a value that uniquely identifies a record. Examples: Phone directories

Direct (Random) Access Records are located by knowing their physical locations or addresses on the device rather than their positions relative to other records. Data stored on a CD device (direct-access) can be accessed either sequentially or randomly.

Types of Files used in an Organization System Following are the types of files used in an organization system: Master file: It contains the current information for a system. For example, customer file, student file, telephone directory. Table file: It is a type of master file that changes infrequently and stored in a tabular format. For example, storing Zipcode. Transaction file: It contains the day-to-day information generated from business activities. It is used to update or process the master file. For example, Addresses of the employees. Temporary file: It is created and used whenever needed by a system. Mirror files: They are the exact duplicates of other files. Help minimize the risk of downtime in cases when the original becomes unusable. They must be modified each time the original file is changed. Log files: They contain copies of master and transaction records in order to chronicle any changes that are made to the master file. It facilitates auditing and provides mechanism for recovery in case of system failure. Archive file: Backup files that contain historical versions of other files.

Documentation Control Documentation is a process of recording the information for any reference or operational purpose. It helps users, managers, and IT staff, who require it. It is important that prepared document must be updated on regular basis to trace the progress of the system easily.

After the implementation of system if the system is working improperly, then documentation helps the administrator to understand the flow of data in the system to correct the flaws and get the system working.

Programmers or systems analysts usually create program and system documentation. Systems analysts usually are responsible for preparing documentation to help users learn the system. In large companies, a technical support team that includes technical writers might assist in the preparation of user documentation and training materials.

Advantages It can reduce system downtime, cut costs, and speed up maintenance tasks. It provides the clear description of formal flow of present system and helps to understand the type of input data and how the output can be produced. It provides effective and efficient way of communication between technical and nontechnical users about system. It facilitates the training of new user so that he can easily understand the flow of system. It helps the user to solve the problems such as troubleshooting and helps the manager to take better final decisions of the organization system. It provides better control to the internal or external working of the system.

Types of Documentations When it comes to System Design, there are following four main documentations: Program documentation System documentation Operations documentation User documentation

The users, system owners, analysts, and programmers, all put combined efforts to develop a user’s guide.

A user documentation should include: A system overview that clearly describes all major system features, capabilities, and limitations. Description of source document content, preparation, processing, and, samples. Overview of menu and data entry screen options, contents, and processing instructions. Examples of reports that are produced regularly or available at the user’s request, including samples. Security and audit trail information. Explanation of responsibility for specific input, output, or processing requirements. Procedures for requesting changes and reporting problems. Examples of exceptions and error situations. Frequently asked questions (FAQs). Explanation of how to get help and procedures for updating the user manual.

System Documentation System documentation serves as the technical specifications for the IS and how the objectives of the IS are accomplished. Users, managers and IS owners need never reference system documentation. System documentation provides the basis for understanding the technical aspects of the IS when modifications are made. It describes each program within the IS and the entire IS itself. It describes the system’s functions, the way they are implemented, each program's purpose within the entire IS with respect to the order of execution, information passed to and from programs, and overall system flow.

It includes data dictionary entries, data flow diagrams, object models, screen layouts, source documents, and the systems request that initiated the project Most of the system documentation is prepared during the system analysis and system design phases. During systems implementation, an analyst must review system documentation to verify that it is complete, accurate, and up-to-date, and including any changes made during the implementation process.

Design Strategies

Top-Down Strategy The top-down strategy uses the modular approach to develop the design of a system. It is called so because it starts from the top or the highest-level module and moves towards the lowest level modules.

In this technique, the highest-level module or main module for developing the software is identified. The main module is divided into several smaller and simpler submodules or segments based on the task performed by each module. Then, each submodule is further subdivided into several submodules of next lower level. This process of dividing each module into several submodules continues until the lowest level modules, which cannot be further subdivided, are not identified.

Structured Design Structured design is a data-flow based methodology that helps in identifying the input and output of the developing system. The main objective of structured design is to minimize the complexity and increase the modularity of a program. Structured design also helps in describing the functional aspects of the system.

In structured designing, the system specifications act as a basis for graphically representing the flow of data and sequence of processes involved in a software development with the help of DFDs. After developing the DFDs for the software system, the next step is to develop the structure chart.

Modularization Structured design partitions the program into small and independent modules. These are organized in top down manner with the details shown in bottom. Thus, structured design uses an approach called Modularization or decomposition to minimize the complexity and to manage the problem by subdividing it into smaller segments.

Advantages Critical interfaces are tested first. It provide abstraction. It allows multiple programmers to work simultaneously. It allows code reuse. It provides control and improves morale. It makes identifying structure easier.

Structured Charts Structured charts are a recommended tool for designing a modular, top down systems which define the various modules of system development and the relationship between