Data Flow Diagram

mywbut. com selective information hang Diagrams (DFDs) 1 mywbut. com Specific Instructional Objectives At the end of this lesson the student will be able to invest the activities carried pop during the structured analysis phase. beg off what a DFD is. Explain why constructing DFDs be important in arriving at a good softwargon design. Explain what a entropy dictionary is. Explain the importance of information dictionary. Identify whether a DFD is balanced. Structured Analysis Structured analysis is used to stomach out the top-down dissolution of a set of high-level ferments visualized in the problem description and to plant them graphically.During structured analysis, functional decomposition of the brass is achieved. That is, each function that the transcription performs is analyzed and hierarchically decomposed into to a greater extent detailed functions. Structured analysis technique is based on the adjacent essential underlying principles Top-down decompos ition approach. Divide and conquer principle. all(prenominal) function is decomposed independently. Graphical inventation of the analysis results employ Data Flow Diagrams (DFDs). Data Flow Diagram (DFD)The DFD ( likewise known as a sing chart) is a hierarchical graphical molding of a system that shows the contrasting work outing activities or functions that the system performs and the info interchange among these functions. Each function is considered as a processing station (or process) that consumes some excitant selective information and produces some output entropy. The system is represented in terms of the input data to the system, various processing carried out on these data, and the output data generated by the system. A DFD impersonate uses a precise limited exit of primitive symbols as shown in fig. 5. 1(a) to epresent the functions performed by a system and the data menses among these functions. 2 mywbut. com External Entity Process Output Data Flow (a) Dat a Store number readnumber validatenumber data-item validnumber (b) data-item readnumber validatenumber validnumber number (c) Fig. 5. 1 (a) Symbols used for designing DFDs (b), (c) co-occurrent and asynchronous data flow Here, two showcases of data flow that expose input and validation of data are considered. In Fig. 5. 1(b), the two processes are directly connected by a data flow. This means that the validate-number process john start only after the readnumber process had supplied data to it.However in Fig 5. 1(c), the two processes are connected through a data store. Hence, the operations of the two bubbles are independent. The showtime one is termed synchronous and the s one asynchronous. Importance of DFDs in a good software package design The main reason why the DFD technique is so normal is probably because of the fact that DFD is a very sincere formalism it is simple to understand and use. Starting with a set of high-level functions that a system performs, a DFD mod el 3 mywbut. com hierarchically represents various sub-functions. In fact, whatsoever hierarchical model is simple to understand.Human mind is such that it can slow understand any hierarchical model of a system because in a hierarchical model, starting with a very simple and see model of a system, different details of the system are soft introduced through different hierarchies. The data flow drawming technique also follows a very simple set of intuitive concepts and rules. DFD is an elegant exemplar technique that turns out to be useful not only to represent the results of structured analysis of a software problem, but also for several(prenominal) other applications such as showing the flow of documents or items in an organization.Data dictionary A data dictionary lists all data items seem in the DFD model of a system. The data items listed include all data flows and the contents of all data stores appearing on the DFDs in the DFD model of a system. A data dictionary lists the purpose of all data items and the definition of all composite data items in terms of their fragment data items. For example, a data dictionary entry may represent that the data grossPay consists of the components regularPay and overtimePay. grossPay = regularPay + overtimePay For the smallest units of data items, the data dictionary lists their denote and their type.Composite data items can be defined in terms of primitive data items using the following data definition operators + denotes composition of two data items, e. g. a+b represents data a and b. ,, represents selection, i. e. any one of the data items listed in the brackets can occur. For example, a,b represents either a occurs or b occurs. () the contents privileged the bracket represent optional data which may or may not appear. e. g. a+(b) represents either a occurs or a+b occurs. represents iterative data definition, e. g. name5 represents five name data. name* represents zero or more instances of name data. rep resents equivalence, e. g. a=b+c means that a represents b and c. = /* */ Anything appearing within /* and */ is considered as a comment. 4 mywbut. com cause 1 Tic-Tac-Toe Computer Game ticktacktoe is a computer plunk for in which a human worker and the computer make alternative departs on a 3? 3 square. A move consists of marking previously unmarked square. The player who first places three square marks along a straight eminence on the square (i. e. along a row, column, or diagonal) wins the game.As soon as either the human player or the computer wins, a pass congratulating the winner should be displayed. If neither player manages to get three consecutive marks along a straight line, but all the squares on the advance are filled up, then the game is drawn. The computer endlessly tries to win a game. display Tic-Tac-Toe Software 0 move Human Player (a) display venire 0. 1 validatemove 0. 2 game move board result checkwinner 0. 4 playmove 0. 3 (b) Fig 5. 2 (a), (b) Level 0 and Level 1 DFD for Tic-Tac-Toe game described in Example 1 5 mywbut. comIt may be recalled that the DFD model of a system typically consists of several DFDs level 0, level 1, etc. However, a sensation data dictionary should capture all the data appearing in all the DFDs constituting the model. Figure 5. 2 represents the level 0 and level 1 DFDs for the tic-tactoe game. The data dictionary for the model is given below. Data dictionary for the DFD model in Example 1 move display game board result integer /*number between 1 and 9 */ game+result board integer9 computer won, human won draw Importance of data dictionaryA data dictionary plays a very important role in any software phylogenesis process because of the following reasons A data dictionary provides a standard terminology for all relevant data for use by the engineers workings in a project. A consistent vocabulary for data items is very important, since in large projects different engineers of the project have a determi nation to use different terms to refer to the same data, which unnecessary causes confusion. The data dictionary provides the analyst with a means to determine the definition of different data structures in terms of their component elements. Balancing a DFD The data that flow into or out of a bubble must advert the data flow at the next level of DFD. This is known as balancing a DFD. The concept of balancing a DFD has been illustrated in fig. 5. 3. In the level 1 of the DFD, data items d1 and d3 flow out of the bubble 0. 1 and the data item d2 flows into the bubble 0. 1. In the next level, bubble 0. 1 is decomposed. The decomposition is balanced, as d1 and d3 flow out of the level 2 diagram and d2 flows in. 6 mywbut. com (a) Level 1 DFD (b) Level 2 DFD Fig. 5. 3 An example showing balanced decomposition 7