An Operating Systems Vade Mecum

252 The User Interface Chapter 7The computer is a convenient place to store a great variety of information. We have seenhow a directory structure assists the user in organizing files and how structures in filescan speed up searches. A typical operating system offers a large number of utility programsfor manipulating information.The easiest form of manipulation affects entire files. The Transfer program that wehave been using as an example exists in some form on every operating system. Not allfunctions are necessarily provided by a single program, but the following operations areoften supported on files.printdisplaycopymoverenamedeletereformatpermit(on a printing device)(on an interactive terminal)(to a new file)(to a new place)(changing character codes, indentation, or headings)(change access rights)In addition, the following operations on directories are supplied:listmakedeleterenamemovepermit(tell which files are in the directory)(a new directory)(an entire directory)(to a new place)(change access rights)Various retrieval methods are often provided for information. For example, utilitiesare often provided to find which files satisfy some criterion. The criterion can bebased on the name of the file, the date on which it was created or modified, or its type(text, load image, and so forth). Lines in text files that match some pattern can beprinted.Sorting is an important activity in many algorithms. Since the best method forsorting depends on the type and number of data, ‘‘sort packages’’ have been built thatcreate the most appropriate sorting program for a particular application.Large-scale database management systems are found in some installations. Theymay allow many users to inspect and modify the database simultaneously. The userinterface to these programs is often a command language specially tailored for formingqueries such as ‘‘find all customers in Indiana who paid their last bill within 1 week ofreceiving it and whose bill was at least twice as high as the average bill.’’Documents are not the only objects that users wish to manipulate interactively.Structure editors allow users to enter and modify such varied objects as printer fonts,VLSI circuit layouts, pictures, stored speech, and file directories. Integrating these variousobject types into a common editing paradigm is a subject of current research.