ABSTRACTION OF DATA FLOW DIAGRAM FOR A C PROGRAM

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1 International Journal of Operations System and Human Resource Management Vol. 2, Nos. 1-2, January-December 2012, pp International Science Press ABSTRACTION OF DATA FLOW DIAGRAM FOR A C PROGRAM Vijaylaxmi Bittal 1, and Manjula Dyavanur 2* Abstract: Data flow diagrams (DFDs) reveal relationships among and between the various components in a program or system. DFDs are an important technique for modeling a system s high-level detail by showing how input data is transformed to output results through a sequence of functional transformations. DFDs consist of four major components: entities, processes, data stores, and data flows. The symbols used to depict how these components interact in a system are simple and easy to understand; however, there are several DFD models to work from, each having its own symbology. In this paper we have given steps for abstraction of data flow diagram for a C program by taking student record as a case study. Keywords: DFD, Abstraction, Context diagram, OMT. 1. INTRODUCTION Data flow diagrams have[1] replaced flowcharts and pseudo code as the tool of choice for showing program design. A DFD illustrates those functions that must be performed in a program as well as the data that the functions will need. A DFD is illustrated in Figure 1 Figure 1: Example 1 DAssistant Professor, Department Of Computer Science, SKSVMACET, Laxmeshwar ,Dist-Gadag 2 * Corresponding Author Lecturer, Department Of Computer Science, SKSVMACET, Laxmeshwar , Dist-Gadag,

2 70 International Journal of Operations System and Human Resource Management 1.1. Defining DFD Components DFDs [2] consist of four basic components that illustrate how data flows in a system: entity, process, data store, and data flow. Entity An entity is the source or destination of data. The source in a DFD represents these entities that are outside the context of the system. Entities either provide data to the system (referred to as a source) or receive data from it (referred to as a sink). Entities are often represented as rectangles (a diagonal line across the right-hand corner means that this entity is represented somewhere else in the DFD). Entities are also referred to as agents, terminators, or source/sink. Process The process is the manipulation or work that transforms data, performing computations, making decisions (logic flow), or directing data flows based on business rules. In other words, a process receives input and generates some output. Process names (simple verbs and dataflow names, such as Submit Payment or Get Invoice ) usually describe the transformation, which can be performed by people or machines. Processes can be drawn as circles or a segmented rectangle on a DFD, and include a process name and process number. Data Store A data store is where a process stores data between processes for later retrieval by that same process or another one. Files and tables are considered data stores. Data store names (plural) are simple but meaningful, such as customers, orders, and products. Data stores are usually drawn as a rectangle with the right hand side missing and labeled by the name of the data storage area it represents, though different notations do exist. Data Flow Data flow is the movement of data between the entity, the process, and the data store. Data flow portrays the interface between the components of the DFD. The flow of data in a DFD is named to reflect the nature of the data used (these names should also be unique within a specific DFD). Data flow is represented by an arrow, where the arrow is annotated with the data name. These DFD components are illustrated in Figure 2 Figure 2: DFD Components

3 Abstraction of Data Flow Diagram for a C Program PROCESS OF DEVELOPING DFD S Data flow diagrams can be expressed as a series of levels. We begin by making a list of business activities to determine the DFD elements (external entities, data flows, processes, and data stores). Next, a contextdiagram is constructed that shows only a single process (representing the entire system), and associated external entities. The Diagram-0, or Level 0 diagram, is next, which reveals general processes and data stores. Following the drawing of Level 0 diagrams, child diagrams will be drawn (Level 1 diagrams) for each process illustrated by Level 0 diagrams Steps for Abstraction of a Data Flow Diagram for a C Program 1. Read the input. 2. Determine the data items. [ which are usually located in documents (but not always).] 3. Determine where they come from and where they go. Construct a table to organize your information, as shown in Table 1 Table 1 Source and Destination for Data Items Data Item Source Destination Need Account Project Analysis Executive Manager ROI Study Presales Proposal Support Manager 4. Determine the system boundaries [In this determining which entities belong internal to the system and which ones are external to the system] 5. All components within the system boundary are included within a single system/process box in the DFD. [External entities lie outside the system boundary, internal entities lie outside the system boundary and internal entities will become locations for process] 6. Next check for a data flow, if there is a flow from external entity to process within a system boundary, make a data flow with a solid line.(in either direction) 7. OR if a data flow from process to data store (in either direction) make a dataflow with solid line between process to data store. 8. OR if a data flow is from process to process means that can only run simultaneously then make a data flow from process to process. 9. Before terminating if you want to express DFD in series of levels // level1 DFD Yes go for step 10, else go to step Identifies the major process and data stores.

4 72 International Journal of Operations System and Human Resource Management 11. Identify or list each incoming and outgoing data flow with a corresponding process that receives generates data. 12. Make sure you refer to your data item table for any missing internal data flows and to identify data stores. [If your table contains documents with the same source and destination, so select only one flow] 13. Identify these processes that only address internal output and outputs and use one process for each source or destination from the DFD. 14. Revising the Level 1 DFD. (a) Check that level1 processes correspond with the major functions. (b) Check level of detail balanced across the DFD. (c) Check that it is possible to merge some processes. (d) Check that it is possible to remove data stores not shared by more than one processes. (e) Check that it is avoided crossed data flow lines making use of duplicated components 15. Terminate Case Study [ external entities and data stores] or not. C program to create a sequential file with atleast 5 records each record having following structure. (Table 2) Table 2 Student Record USN Name Marks 1 Marks 2 Marks 3 + ve integer 25 character + ve integer + ve integer +ve integer #include<stdio.h> #include<process.h> #include<string.h> typedef struct int usn; char name[20]; int marks1; int marks2; int marks3; STUDENT; void main() STUDENT st; char fname[10]; FILE *fp;

5 Abstraction of Data Flow Diagram for a C Program 73 int key_usn; int flag; int choice; printf( enter the file name\n ); scanf( %s,fname); for(;;) printf( 1:insert Record 2: Search record 3: Display record 4: Quit\n ); scanf( %d,&choice); switch(choice) case 1: fp=fopen(fname, a+ ); if(fp==null) printf( Fopen failed\n ); Append_record(); fclose(fp); case 2:fp= fopen(fname, r ); if(fp==null) printf( File open failed\n ); printf( Enter USN: ); scanf( %d,&key_usn); flag=search_record(key_usn, fp); if(flag==0) printf( unsuccessfull search\n ); else printf( successful search\n ); fclose(fp); case 3:fp=fopen(fname, r ); if(fp==null) printf( File opened failed\n );

6 74 International Journal of Operations System and Human Resource Management display_records(fp); fclose(fp); default: exit(0); int search_record(int key_usn, FILE *fp) STUDENT st; for(;;) fscanf(fp, %d,%s,%d,%d,%d,&st.usn,st.name,&st.marks 1,&st.marks2,&st.marks3); if((feof(fp)) if(key_usn==st.usn) return 1; return 0; void append_record(file *fp) STUDENT at; printf ( USN: ); scanf( %d,&st.usn); printf( name ); scanf( %d,&st.usn); printf( marks1: ); scanf( %d, &st.marks1); printf( marks2 ); scanf( %d,&st.marks2); printf( marks3 ); scanf( %d,&st.marks3); fprintf(fp, %d,%s,%d,%d,%d,&st.usn,st.name,&st.marks1,&st.marks2,&st.marks3); void display_records(file *fp)

7 Abstraction of Data Flow Diagram for a C Program 75 STUDENT st; printf( USN NAME MARKS1 MARKS2 MARKS 3 ); for(;;) fscanf(fp, %d,%s,%d,%d,%d,&st.usn,st.name,&st.marks1,&st.marks2,&st.marks3); if(feof(fp)) printf( %d,%s,%d,%d,%d,st.usn,st.name,st.marks1,st.mar ks2,st.marks3); Now Apply Steps to the Above Case Study 1. Read the input. 2. Determining data items. In this program data items are mainly the user and program for sequential file. 3. Determine where they come and where they go. Here user is an external entity and sequential program is a process. 4. Determining system boundaries. ( as shown in Figure 3) Figure 3: Determining System Boundaries 5. This program contain 3 more processes but they are kept in a single process box that is sequential program box [Developing level0 DFD] 6. There is a flow from user to a sequential program process will take a flow between in either direction. 9. Suppose we want to represent DFD in series of levels,then goto step Identify a major process and data items. Major process - Sequential program Sequential program - append_record(process) - display_records(process) - search_record(process) - student_record( data store)

8 76 International Journal of Operations System and Human Resource Management 11. Listing incoming and outgoing data flow. Table 3 Incoming and Outgoing Data Flow Source User append_record user student-record user student-record Destination append_record student_record display_record display_record serach_record serch_record 12. Make sure that we referring to these data item table for any missing internal data flows and to identify data store. 13. The processes append_record display_record search_record The generated DFD for above steps is shown in Figure Apply the revising steps for level1 DFD. 15. Terminate. Figure 4: Level 1 DFD

9 Abstraction of Data Flow Diagram for a C Program STEPS IN OBJECT ORIENTED ANALYSIS The first step in OOA is often the identification of important classes, which is done by identifying the nouns in the requirement specification. Many times, classes are defined from tangible things, roles, or incidents. Analysis also includes defining object attributes and object and class or other relationships. Analysis also attempts to identify the behavior of objects and classes as well as data flow between objects OMT Modeling The output of OMT is a three-dimensional view (from three different models) of the system that stays the same during the transition from analysis to design. The Object Model describes the static system components and is modeled using object diagrams. The Dynamic Model describes the dynamic system components that change over time and are modeled using state diagrams. The Functional Model describes operations performed on data in a system and uses data flow diagrams. 4. CONCLUSION Data flow diagramming is a highly effective technique for showing the flow of information through a system. DFDs are used in the preliminary stages of systems analysis to help understand the current system and to represent a required system. We have given steps for abstraction of DFD for C program, verified these steps for case study and also given brief steps for object oriented analysis. DFDs are extremely useful in systems analysis as they help structure the steps in object-oriented design and analysis. Because DFDs and object technology share the same syntax constructs, DFDs are appropriate for the OO domain only. REFERENCES [1] Perry, Greg. Sams Teach Yourself Beginning Programming in 24 Hours, Sams Publishing, [2] Le Vie, Jr., Donald, An ecommerce Primer for Technical Communicators, STC Proceedings of the 47th Annual Conference, Donald.

System Analysis and Design. Data Flow Diagram. System Analysis and Design

System Analysis and Design. Data Flow Diagram. System Analysis and Design Data Flow Diagram 1 Data Flow diagram The dataflow diagram is a modeling tool that allows us to picture a system as a network of functional processes, connected to one another by pipelines and holding