Basic File-system Organization

This thinker observed that all the books no matter how diverse they might be, are made up out of the same elements: the space, the period, the comma, the twenty-two letters of the alphabet. He also alleged the fact which travellers have confirmed: In the vast Library there are no two identical books. From these two incontrovertible premises he deducted that the Library is total and that its shelves register all the possible combinations of the twenty-odd orthographical symbols (a number which, though extremely vast, is not infinite): in other words, all that is given to express, in all languages. Everything: the minutely detailed history of the future, the archangels' autobiographies, the faithful catalogue of the Library, thousands and thousands of false catalogues, the demonstration of fallacy of the true catalogue,. .. Jorge Luis Borges from " The Library of Babel " , a story in the " Labyrinths " 3-0 INTRODUCTION The primary features needed in systems that store large amounts of data are fast access for retrieval, convenient update, and economy of storage. Important secondary criteria are the capability to represent real world information structures, reliability, protection of privacy, and the maintenance of integrity. All these criteria tend to conflict with each other. The choice of the file organization method determines the relative suitability of a system according to all these criteria. We will initially evaluate files according to the basic criteria. A good match of the capabilities provided by the file system to priorities assigned to the criteria, as determined by the objectives for the database, is vital to the success of the resulting system. The number of possible alternatives for the organization of files is nearly unlimited. To make the 73 74 Basic File-System Organization selection process manageable, we will describe and evaluate fundamental file-design alternatives. Most structures used in practice either fall into one of these categories or can be reduced to combinations of these methods. These fundamental types are closely related to systems in actual use. The collection of these six does not represent a mathematically minimal set of independent file organization methods. The selected methods are also reasonable in terms of the secondary criteria, i.e., they are fairly reliable and easy to analyze and implement. The six fundamental types of files are covered in the chapters as follows: Sections 3-1 and 3-2: Two basic file types, without ancillary access structures: 3-1 The pile …