Concepts
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Its main advantages are:1 it is easy to implement;2 it provides fast access to the next record using lexicographic order
...Its disadvantages:1 it is difficult to update inserting a new record may require moving a large proportion of the file;2 random access is extremely slow
...Sometimes a file is considered to be sequentially organised despite the fact that it is not ordered according to any key
...Inverted files The importance of this file structure will become more apparent when Boolean Searches are discussed in the next chapter
...An inverted file is a file structure in which every list contains only one record
...Index sequential files An index sequential file is an inverted file in which for every keyword Ki,we have ni hi 1 and a 11 <a 21
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is no K 3 list,the field reserved for its pointer could well have been omitted
...The multi list is designed to overcome the difficulties of updating an inverted file
...Cellular multi lists A further modification of the multi list is inspired by the fact that many storage media are divided into pages,which can be retrieved one at a time
...At this point the full power of the notation introduced before comes into play
...Ki,ni,hi,ai 1,...where the hi have beenpicked to ensure that a Ki list does not cross a page boundary
...Ring structures A ring is simply a linear list that closes upon itself
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