20-10-2012, 04:47 PM
ONLINE PRISON MANAGEMENT SYSTEM
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DATA FLOW DIAGRAM
A data flow diagram (DFD) or a bubble chart is a graphical tool for structured analysis. It was De Marco (1978) and Gane And Sarson (1979) who introduced DFD.DFD models a system by using external entities from which data flows to a process, which transforms the data and creates, output-data-flows which go to other process or external entities or files. Data in files may also flow to processes as arrows.
There are various symbols used in the DFD. Bubbles represent the processes. Named arrows indicate the data flow. External entities are represented by rectangles and are outside the system such as vendors or customers with whom the system interacts. They either supply or consume data. Entities supplying data are named as sources and those that consume data are called sinks. Data are stored in a data store by a process in the system. Each component in a DFD is labeled with a descriptive name. Process names are further identified with a number . DFD’s can be hierarchically organized, which helps in partitioning and analyzing large systems. As a first step one DFD can depict an entire system, which gives the overview. This is called context diagram of Level 0 DFD.
Context diagram can be further expanded. The successive expansion of the DFD from
the context diagram to those giving more details is known as leveling of DFD. Thus a top down approach is used, starting with an overview and then working out the details.
The main merit of DFD is that it can provide an overview of what data a system would process, what transformation of data are done, what files are used, and where results flow.
A DFD does not show procedural information. A leveled DFD set has a starting DFDs that is very abstract representation of the system, identifying the major inputs and outputs and major processes in the system. Then each process is defined and a DFD is drawn for each process.
Data Flow Diagrams are made up of a number of symbols, which represents system components. Data flow modeling method uses four kinds of symbols, which are used to represent four kinds of system components. These are
• Process
• Data stores
• Data flows
• External entity
Process
Process shows the work of the system. Each process has one or more data inputs and produce one or more data outputs. Processes are represented by rounded rectangles in Data Flow Diagram. Each process has a unique name and number. This name and number appears inside the rectangle that represents the process in a Data Flow Diagram.
Data Stores
A data store is a repository of data. Processes can enter data, into a store or
retrieve the data from the data store. Each data has a unique name.
Data Flows
Data flows show the passage of data in the system and are represented by lines joining system components. An arrow indicates the direction of flow and the line is labeled by name of the data flow.
External Entity
External entities are outside the system but they either supply input data into the system or use other systems output. They are entities on which the designer has control. They may be an organizations customer or other bodies with which the system interacts. External entities that supply data into the system are sometimes called source. External entities that use the system data are sometimes called sinks. These are represented by rectangles in the Data flow Diagram.
Four basic symbols are used to construct data flow diagrams. They are symbols that represent data source, data flows, and data transformations and data storage. The points at which data are transformed are represented by enclosed figures, usually circles, which are called nodes.
DATABASE DESIGN
The data design transforms the information domain model created during analysis into the data structures that will be required to implement the software. The data objects and relationships defined in the entity relationship diagram and the detailed data content depicted in the data dictionary provide the basis for the data design activity.
The overall objective in the development of database technology has been to treat data as an organizational resource and as an integrated whole. Database Management System allows data to be protected and organized separately from other resources. Database is an integrated collection of data. This is the difference between logical and physical data.
The organization of data in the database aims to achieve three major objectives:
Data integration
Data independence
Data integrity
The databases are implemented using a DBMS package. Each particular DBMS has unique characteristics and general techniques for database design. There are 6 major steps in design process. The first 5 steps are usually done on paper and finally the design is implemented.
• Identify the table and relationships
• Identify the data that is needed for each table and relationship
• Resolve the relationship
• Verify the design
• Implement the design.
The proposed system ‘ONINE TELEPHONE MANAGEMENT SYSTEM’ stores the information relevant for processing in the Microsoft SQL Server Management Studio Express (Microsoft SQL Server2008). The database uses tables for storage. A table also contains records, which is a set of fields. All records, in a table have the same set of fields with different information.
The design of the database measures the efficiency of the system. The background used in this application is Microsoft SQL Server2008, which provides databases and tables for storage and queries for retrieving data from the database.
• To avoid restructuring of data when new application requirements arises