Organization of Records in Files

Organization of Records in Files

There are three commonly used approaches of organizing records in file -

(1) Heap file organization: Any record can be placed anywhere in the file where there is a space. There is no ordering for placing the records in the file. Generally single file is used.

(2) Sequential file organization: Records are stored in sequential order based on the value of search key.

(3) Hashing file organization: A hash function is used to obtain the location of the record in the file. Based on the value returned by hash function, the record is stored in the file.

Sequential File Organization

The sequential file organization is a simple file organization method in which the records are stored based on the search key value.

• For example - Consider following set of records stored according to the RollNo of student. Note that we assume here that the RollNo is a search key.

Now if we want to insert following record

Then, we will insert it in sorted order of RollNo and adjust the pointers accordingly.

• However, maintaining physical sequential order is very difficult as there can be several insertions and deletions.cos le

• We can maintain the deletion by next pointer chain.

• For insertion following rules can be applied -

  • If there is free space insert record there.

  • If no free space, insert the record in an overflow block.

  • In either case, pointer chain must be updated.

Multi-table Clustering File Organization

In a multitable clustering file organization, records of several different relations are stored in the same file.

For example - Following two tables Student and Course

The multitable clustering organization for above tables is,

This type of file organization is good for join operations such as Student Course. This file organization results in variable size records.

The pointer chain can be added to the above records to keep track of address of next record. It can be as shown in following Fig. 4.3.2.