Picture files for hierarchically structured pictures

Abstract For a high-level graphics programming language like PASCAL/Graph[1, 2] which allows a hierarchical structure in the representation of pictures, there must exist an appropriate concept for mapping them on sequential files, and vice versa. This paper describes the internal implementation of pictures in PASCAL/Graph by the picture graph. An important feature is the common subpicture, which means picture information can be reused for several higher level pictures without being duplicated. The representation of such pictures on external files, called picture files, is explained, too. Attention is directed to the correct conversion and reconversion between internal and external representation, so that the status of common subpictures is preserved without any exception. This concept allows many effective operations in constructing pictures as well as storing pictures in a very efficient way, both in main memory and on files. The simple GKS metafile cannot handle these complexly structured pictures; therefore, the more complicated form of picture files (metafiles) is necessary.