Technical Interview Questions and Answers :: DBMS
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The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage definition language
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This language that enables user to access or manipulate data as organized by the appropriate data model.
* Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
* vNon-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.
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It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
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It executes low-level instruction generated by compiler.
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It interprets DDL statements and record them in tables containing metadata.
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The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.
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The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.
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It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.
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It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.
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The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL
The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.