Systems Documentation Techniques Professor Merle Martin Professor Yan Xiong College of Business CSU Sacramento 2/6/023 Agenda Why Document System Data Flow Diagrams Flowcharts Difference between DFDs and Flowcharts Why Document Systems? User confidence that you understand system Successive refinement of detail down to programming level Ease of Program Maintenance, System Modification, Reengineering, and Replacement Why Document Systems? Problem Solving Humans solve complex problems by breaking them into smaller and smaller modules until they fit into the human mind solving the modular sub-problems aggregating small solutions into total solution Agenda Why Document Accounting Information Systems Data Flow Diagrams (DFDs) Flowcharts Difference between DFD Data Flow Diagrams Data flow diagram (DFD) graphically describes flow of data within any system Used to document existing systems and to plan and design new ones No ideal way to develop a DFD judgment within standard rules Data Flow Diagrams DFD composed of only four elements: Data sources and destinations: External Entities Another organization/organization unit which exchanges data with the focal system A person who interacts with the system (customer of a banking system) Another information system Data Flows Processes Data Stores: Temporary or permanent repository of data DFD Symbols INPUT PROCESS OUTPUT External Data Data External Process Entity Flow Flow Entity Source Sink Data Flow Data Store DFD Symbols Payment 1.1 deposit Customer Process Bank Payment Source Sink Remittance data Customer File Data Flow Diagrams Explosion Data flow diagrams subdivided into successively lower levels in order to provide increasing amounts of detail This decomposition process is called “explosion” Data Flow Diagram Explosion Context Level Ist Level Explosion 2nd Level Explosion Succeeding levels as necessary Until reach primitive level Ready to code Context Diagram Includes only External Entities Data Flows All elements included on Context Diagram must be included somewhere on lower level diagrams Data stores rarely included! Context Diagram Why discourage Data Stores on Context Diagram? Author includes them Context Diagram shows interaction of your system with outside world Data Stores are INSIDE your system, not in outside world Purchase Purchase Inventory Requisition Order Vendor System 0 Order Purcha- Receiving Entry System Special sing Purchase System Order Order Notification Context Diagram 1st Level Explosion Also includes all data flows and external entities Now data stores are added Excellent means of confirming understanding of system between analyst and client Each process will be exploded into lower level DFDs Ist Level Explosion Purchase Inventory 1 Requisition Edit Inventory Order Problem Approved Orders Order 2 Order Entry Set Ship Mode Vendor Vendor Draft P.O 3 P.Order P.O. Copy Prepare P.O.Noti- Receiving P.O. fication 2nd and Succeeding Levels Must be consistent with parent DFD Same external entities Same data stores Same data flows 2nd Level Explosion (Process 1) Purchase 1.1 Requisition Log-in Inventory Order Logged-in Inventory Order 1.2 Order Entry Edit Problem Order Orders Log-in Edited #s Order 1.3 Process Approve Approved 2.1 Order Order DFD Rules -- Process A. No process can have only outputs (a miracle) B. No process can have only inputs (a black hole) C. Verb phrase labels DFD Rules -- Data Store D. Data cannot move directly from one data store to another data store -- it must be moved by a process. E. Data cannot move directly from an outside source to a data store -- it must be moved by a process. F. Data cannot move directly to an outside sink from a data store -- it must be moved by a process. G. Noun phrase label DFD Rules -- Source / Sink H. Data cannot move directly from a source to a sink. It must be moved by a process. I. Noun phrase label DFD Rules -- Data Flow J. A data flow has only one direction of flow between symbols; a data flow may flow in both directions to and from a data store (usually two symbols) K. A fork in a data flow means that exactly the same data goes to two different processes or data stores. DFD Rules -- Data Flow L. A data flow cannot go directly back to the same process it leaves M. A data flow to a data store means update (delete or change) N. A data flow from a data store means retrieve or use O.Noun phrase label Other DFD Issues Two additional guidelines Inputs to a process are different from outputs of that process Every process in a DFD has a unique name Exercise Draw a Context Diagram and a 1st level explosion Current System Description for the payroll system at No-Wear Products. Time data are recorded in each department using time cards and clocks. The time data are sent to the payroll by different departments. Payroll clerks review the time data for their completeness. Human resources send the payroll data on personnel changes, such as increases in pay rates and new employees. Payroll clerks update the payroll file based on these changes. At the end of the period, payroll clerks enter the time card data into the payroll file for processing. The payroll supervisor reviews the file and makes necessary corrections. Payroll clerks send the direct payments to the bank and also the direct deposit slips to the departments. Agenda Why Document Accounting Information Systems Data Flow Diagrams Flowchart Difference between DFD and Flowchart Flowcharts A flowchart is an analytical technique used to describe some aspect of an information system in a clear, concise, and logical manner. Flowcharts use a standard set of symbols to pictorially describe transaction processing procedures. Flowchart Symbols Flowcharting symbols can be divided into the following four categories: 1 Input/output symbols 2 Processing symbols 3 Storage symbols 4 Flow and miscellaneous symbols Flowcharting Symbols: Input Output Symbols Symbol Name Document Online keying Display Input/output; Journal/ledger Flowchart Symbols: Processing symbols Symbol Name Manual operations Computer processing Auxiliary operation Flowchart Symbols: Storage Symbols Symbol Name Magnetic disk Magnetic tape Flowchart Symbols: Flow and miscellaneous Symbols Symbol Name Document or processing flow On-page connector Off-page connector Terminal Decision What are Document Flowcharts? A document flowchart illustrates the flow of documents and information between areas of responsibility within an organization. A document flowchart is particularly useful in analyzing the adequacy of control procedures. Flowcharts that describe and evaluate internal controls are often referred to as internal control flowcharts. What are Computer System Flowcharts? System flowcharts depict the relationship among the input, processing, and output of an AIS. A system flowchart begins by identifying both the inputs that enter the system and their origins. The input is followed by the processing portion of the flowchart. What are Computer System Flowcharts? The resulting new information is the output component. System flowcharts are an important tool of system analysis, design, and evaluation. What are Computer System Flowcharts? Input Storage Process Output What are Program Flowcharts? A program flowchart describes the specific logic to perform a process shown on a systems flowchart. A flow line connects the symbols and indicates the sequence of operations. The processing symbol represents a data movement or arithmetic calculation. What are Program Flowcharts? Input data If a condition is met No Yes Perform calculation Update record What are Program Flowcharts? The input/output symbol represents either reading of input or writing of output. The decision symbol represents a comparison of one or more variables and the transfer of flow to alternative logic paths. All points where the flow begins or ends are represented by the terminal symbol. Flowchart for Processing Credit Orders Enter Start sales order Approved No Reject for credit? order Yes Inventory No Back- available? order Yes Fill order Stop Example-Flowcharts The Dewey Construction Company processes its payroll transactions to update both its payroll master file and its work-in-process master file in the same computer run. Both the payroll master file and the work-in-process master file are maintained on disk and accessed directly. Data to be input to this system are keyed onto a tape using a key-to-tape encoder. This tape is then processed to update the files. This processing run also produces a payroll register on magnetic tape, employee paychecks and earnings statements, and a printed report listing error transactions and summary information. Prepare a system flowchart of the process described. Agenda Why Document Accounting Information Systems Data Flow Diagrams Flowchart Difference between DFD and Flowchart Differences Between DFDs and Flowcharts DFDs emphasize the flow of data and what is happening in a system, whereas a flowchart emphasizes the flow of documents or records containing data. A DFD represents the logical flow of data, whereas a flowchart represents the physical flow of data. Differences Between DFDs and Flowcharts Flowcharts are used primarily to document existing systems. DFDs, in contrast, are primarily used in the design of new systems and do not concern themselves with the physical devices used to process, store, and transform data.
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