by user267658217

Before creating a logic or process flowchart, the designer must understand the algorithm or procedure. The necessary information might be compiled from direct observation, extracted from existing documentation, or derived from the information gathered during the problem definition (Part II) and/or systems analysis (Part IV) stages of the system development life cycle.

Other tools for documenting or planning routines or processes include Nassi-Shneiderman charts (# 56), decision trees (# 57), decision tables (# 58), pseudocode (# 59), structured English (# 60), and input/process/output (IPO) charts (# 64). A routine often exists in the context of a larger program. Tools for documenting or planning program structure include structure charts (# 63) and HIPO (# 64).

Logic flowcharts are sometimes confused with system flowcharts (# 37). A system flowchart documents the physical relationships between a system’s physical components. A logic flowchart shows the flow of logic, control, or data through a routine or a procedure.

55.4 Concepts

A logic or process flowchart uses seven standard symbols (Figure 55.1). A terminator marks the beginning or end of the flowchart. A process symbol indicates an operation that changes or manipulates data in some way (e.g., arithmetic, move, or copy). A data symbol (a parallelogram) indicates an operation that inputs or outputs data. A diamond indicates a decision. A connector (a small circle) means that the logic is continued at another place on the same page. An off-page connector (home plate) indicates that the logic is continued on another page. A rectangle within a rectangle indicates a predefined process (or subroutine).

Figure 55.1  Standard flowcharting symbols.

The symbols are linked by flowlines that show the sequence and direction of flow. By convention, logic flows from the top down and from left to right, and arrowheads are added to the flowlines to indicate deviations from this standard pattern. Arrowheads make a flowchart easier to read even when the direction of flow follows convention.

55.4.1 Program logic

Flowcharts with multiple entry or exit points are difficult to follow and can easily be misinterpreted. As a general rule, each routine or process should have a single entry point and a single exit point.

Program logic can be expressed as combinations of three basic patterns: sequence, decision, and repetition (# 62). A program is composed of combinations of these three basic structures.

The sequence pattern (Figure 55.2) implies that the logic is executed in