By S. M. Deen (auth.)
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Midsquare Method Here the value of the key is squared and the central digits of the square are used as the transformed key. Assume that we have a 5 digit key for a file with 2000 buckets. 4 Therefore 139 is the bucket number. Shifting Let us assume that the key is 64012418. Now split the key in the middle into two parts, 6401 and 2418. We can now add these to the middle of the key to yield the transformed key as follows 6401 : 2418 64 : 01 24 I 18 transformed key = 89 43 Now we can normalise the value of the transformed key to give the address.
5 INVERTED FILES The files discussed so far are commonly used in data processing and are referred to as the regular files. Their organisation is simple, each record being characterised by a single key by means of which any of the records can be related. Departure from this involves a complex organisation where a record can be accessed either through multiple keys or through pointers linking the related records. The first of these is the inverted file organisation which permits multiple keys per record.
This is why many Data Base Systems, including the Codasyl model do not allow the direct representation of a network structure; instead a network is divided into two 1 :N relationships, one owned by the first record type and the other by the second record type as described below. 10. All we have done is to divide the 7 datasets into two types of Data Base Organisation 45 group, one type being owned by the occurrences of the Course records and the other type by the occurrences of the Student records.
Fundamentals of Data Base Systems by S. M. Deen (auth.)