Jackson chart
The Jackson Structured Programming is a hierarchical design methodology for software systems. This methodology was introduced starting from 1975 by Michael A. Jackson. Jackson developed thereby an approach based on graphic elements, which is particularly suitable for tasks with large, ordered data sets - i.e. for data-oriented algorithms.
The basic principle of the methodology is to make the structure of the input and output data the starting point of the design, and to derive the actual software structure from this by simple transformation.
Starting point of the methodical beginning of Jackson was on the one hand that for the description of simple data structures as well as like from software structures the same structuring elements can be used; these are in particular the sequence (stringing together), iteration(repetition) and selection (selection).
On the other hand the method of Jackson is based on the thesis that an algorithm and/or a software structure follows in all parts the structure of the input and output data.
For the representation of software and data structures Jackson specified its own structuring notation. In all basic notations between the block "A" and blocks "B", and/or "B", "C" and "D" an "exists-of" relation exists. This allows the construction of hierarchical structures.
The Jackson method includes the following design steps:
- Examine the data structures at the input and output of the task block.
- Superimpose the input data structure with the output data structure.
If there is a correspondence between the components of both data structures, continue with the 3rd design step. In the case of a so-called structure break, i.e. with missing correspondence between the components of both data structures, the problem must be divided on two programs, which are linked over an intermediate file, which is compatible to both data structures.
- Develop the basic structure of the software compatible with both data structures analogously to these data structures.
- Assign the necessary operations to the structure blocks of the software.
The Jackson methodology lost in the age of the object-oriented programming meaning, since it cannot represent the constructs possible with modern programming languages. In addition, the methodology is not applicable with regard to relational databases.