A relational schema needs to maintain data about the data called as metadata. Metadata about the relations is stored in the Data dictionary.

Name of the relation, Domains and lengths of attributes and Integrity constraints all must be stored in the data dictionary.

The full form of LRU is Least Recently Used. In this, the least recently used program is substituted by the new request.

Heap file organization means that any record can be placed wherever there is space for that record. There is no ordering of records. Typically there is a single file for each relation.

Sequential file organization means that Records are stored in a sequential order according to a search key. The records are ordered.

A search key in sequential file organization is any attribute or a set of attributes that need not be a primary key or even a superkey.

Data dictionary is also called as System Catalog.

A multitable clustering file organization stores the related records of two or more relations in each block. This allows us to read records that satisfy a join condition by using one block read.

The subsystem responsible for the allocation of buffer space is called as buffer manager. Programs on the database make requests to the buffer manager and it in in turn allocates the buffer space.

Hashing file organization means that a hash function is computed on some attribute and that decides the block. The result of the hash function specifies which block of the file the record should be placed in.