Nevertheless, it is worth taking seriously the trend away from user knowledge of file structures, a trend that has been stimulated considerably by attempts to construct a theory of data[8,9]. This approach works as one might expect: data is represented in the form of hierarchies.

There are a number of proposals for dealing with data at an abstract level. As it is rather difficult to cope with general relations, various levels (three in fact) of normalisation have been introduced restricting the kind of relations allowed. Although it is more restrictive than the relational approach it often seems to be the natural way to proceed.

It is this logical aspect that we will concentrate on.

The physical organisation is much more concerned with optimising the use of the storage medium when a particular logical structure is stored on, or in it.

Lurking in the background of any discussion of file structures nowadays is always the question whether data base technology will overtake all.

Thus it may be that any application in the field of library automation and information retrieval will be implemented through the use of some appropriate data base package.

This is certainly a possibility but not likely to happen in the near future. One is that data base systems are general purpose systems whereas automated library and retrieval systems are special purpose.

Normally one pays a price for generality and in this case it is still too great.

I shall (on the whole) follow Hsiao and Harary[1] whose terminology is perhaps slightly non-standard but emphasises the logical nature of file structures.

A further advantage is that it enables me to bridge the gap between data management and document retrieval easily.

A few other good references on file structures are Roberts[2], Bertziss[3], Dodd[4], and Climenson[5].

Logical or physical organisation and data independence There is one important distinction that must be made at the outset when discussing file structures.

And that is the difference between the logical and physical organisation of the data.