04-10-2012, 05:27 PM
SYSTEM DESIGN DOCUMENT
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INTRODUCTION
Purpose and Scope
This section provides a brief description of the Systems Design Document’s purpose and scope.
Project Executive Summary
This section provides a description of the project from a management perspective and an overview of the framework within which the conceptual system design was prepared. If appropriate, include the information discussed in the subsequent sections in the summary.
System Overview
This section describes the system in narrative form using non-technical terms. It should provide a high-level system architecture diagram showing a subsystem breakout of the system, if applicable. The high-level system architecture or subsystem diagrams should, if applicable, show interfaces to external systems. Supply a high-level context diagram for the system and subsystems, if applicable. Refer to the requirements trace ability matrix (RTM) in the Functional Requirements Document (FRD), to identify the allocation of the functional requirements into this design document.
1.2.2 Design Constraints
This section describes any constraints in the system design (reference any trade-off analyses conducted such, as resource use versus productivity, or conflicts with other systems) and includes any assumptions made by the project team in developing the system design.
Future Contingencies
This section describes any contingencies that might arise in the design of the system that may change the development direction. Possibilities include lack of interface agreements with outside agencies or unstable architectures at the time this document is produced. Address any possible workarounds or alternative plans.
Document Organization
This section describes the organization of the Systems Design Document.
Points of Contact
This section provides the organization code and title of the key points of contact (and alternates if appropriate) for the information system development effort. These points of contact should include the Project Manager, System Proponent, User Organization, Quality Assurance (QA) Manager, Security Manager, and Configuration Manager, as appropriate.
Project References
This section provides a bibliography of key project references and deliverables that have been produced before this point.
Glossary
Supply a glossary of all terms and abbreviations used in this document. If the glossary is several pages in length, it may be included as an appendix.
SYSTEM ARCHITECTURE
In this section, describe the system and/or subsystem(s) architecture for the project. References to external entities should be minimal, as they will be described in detail in Section 6, External Interfaces.
System Hardware Architecture
In this section, describe the overall system hardware and organization. Include a list of hardware components (with a brief description of each item) and diagrams showing the connectivity between the components. If appropriate, use subsections to address each subsystem.
System Software Architecture
In this section, describe the overall system software and organization. Include a list of software modules (this could include functions, subroutines, or classes), computer languages, and programming computer-aided software engineering tools (with a brief description of the function of each item). Use structured organization diagrams/object-oriented diagrams that show the various segmentation levels down to the lowest level. All features on the diagrams should have reference numbers and names. Include a narrative that expands on and enhances the understanding of the functional breakdown. If appropriate, use subsections to address each module.
Internal Communications Architecture
In this section, describe the overall communications within the system; for example, LANs, buses, etc. Include the communications architecture(s) being implemented, such as X.25, Token Ring, etc. Provide a diagram depicting the communications path(s) between the system and subsystem modules. If appropriate, use subsections to address each architecture being employed.
FILE AND DATABASE DESIGN
Interact with the Database Administrator (DBA) when preparing this section. The section should reveal the final design of all database management system (DBMS) files and the non-DBMS files associated with the system under development. Additional information may add as required for the particular project. Provide a comprehensive data dictionary showing data element name, type, length, source, validation rules, maintenance (create, read, update, delete (CRUD) capability), data stores, outputs, aliases, and description. Can be included as an appendix.
Database Management System Files
This section reveals the final design of the DBMS files and includes the following information, as appropriate (refer to the data dictionary):
• Refined logical model; provide normalized table layouts, entity relationship diagrams, and other logical design information
• A physical description of the DBMS schemas, sub-schemas, records, sets, tables, storage page sizes, etc.
• Access methods (such as indexed, via set, sequential, random access, sorted pointer array, etc.)
• Estimate of the DBMS file size or volume of data within the file, and data pages, including overhead resulting from access methods and free space
• Definition of the update frequency of the database tables, views, files, areas, records, sets, and data pages; estimate the number of transactions if the database is an online transaction-based system
Non-Database Management System Files
In this section, provide the detailed description of all non-DBMS files and include a narrative description of the usage of each file—including if the file is used for input, output, or both; if this file is a temporary file; an indication of which modules read and write the file, etc.; and file structures (refer to the data dictionary). As appropriate, the file structure information should:
• Identify record structures, record keys or indexes, and reference data elements within the records
• Define record length (fixed or maximum variable length) and blocking factors
• Define file access method—for example, index sequential, virtual sequential, random access, etc.
• Estimate the file size or volume of data within the file, including overhead resulting from file access methods
• Define the update frequency of the file; if the file is part of an online transaction-based system, provide the estimated number of transactions per unit time, and the statistical mean, mode, and distribution of those transactions
HUMAN-MACHINE INTERFACE
This section provides the detailed design of the system and subsystem inputs and outputs relative to the user/operator. Any additional information may be added to this section and may be organized according to whatever structure best presents the operator input and output designs. Depending on the particular nature of the project, it may be appropriate to repeat these sections at both the subsystem and design module levels. Additional information may be added to the subsections if the suggested lists are inadequate to describe the project inputs and outputs.
Inputs
This section is a description of the input media used by the operator for providing information to the system; show a mapping to the high-level data flows described in Section 1 .2.1, System Overview. For example, data entry screens, optical character readers, bar scanners, etc. If appropriate, the input record types, file structures, and database structures provided in Section 3, File and Database Design, may be referenced. Include data element definitions, or refer to the data dictionary.
Provide the layout of all input data screens or graphical user interfaces (GUTs) (for example, windows). Provide a graphic representation of each interface. Define all data elements associated with each screen or GUI, or reference the data dictionary.
This section should contain edit criteria for the data elements, including specific values, range of values, mandatory/optional, alphanumeric values, and length. Also address data entry controls to prevent edit bypassing.