DBMS INTERVIEW -3
QUES What is Data Storage - Definition Language?
ANSWER:
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.
QUE What is DML (Data Manipulation Language)?
ANS This language that enable user to access or manipulate data as organised by appropriate data model.
1) Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
2 ) Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.
QUES What is VDL (View Definition Language)?
ANS It specifies user views and their mappings to the conceptual schema.
QUES What is DML Compiler?
ANS It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
QUES What is Query evaluation engine?
ANS It executes low-level instruction generated by compiler.
QUES What is DDL Interpreter?
ANS It interprets DDL statements and record them in tables containing metadata.
QUES What is Record-at-a-time?
ANS 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.
QUES What is Set-at-a-time or Set-oriented?
ANS 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.
QUES What is Relational Algebra?
ANS 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.
QUES What is Relational Calculus?
ANS 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.
QUES How does Tuple-oriented relational calculus differ from domain-oriented relational calculus
ANS 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.
QUES What is normalization?
ANS It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties
1) Minimizing redundancy
2) Minimizing insertion, deletion and update anomalies.
QUES What is Functional Dependency?
ANS A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.
QUES When is a functional dependency F said to be minimal?
ANS 1) Every dependency in F has a single attribute for its right hand side.
2) We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.
3) We cannot remove any dependency from F and still have set of dependency that is equivalent to F.
QUES What is Multivalued dependency?
ANS Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
1 ) t3[x] = t4[X] = t1[X] = t2[X]
2) t3[Y] = t1[Y] and t4[Y] = t2[Y]
3) t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
QUES What is Lossless join property?
ANS It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
QUES What is 1 NF (Normal Form)?
ANS The domain of attribute must include only atomic (simple, indivisible) values.
QUES What is Fully Functional dependency?
ANS It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
QUES What is 2NF?
ANS A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
QUES What is 3NF?
ANS A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
1) X is a Super-key of R.
2) A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.
ANSWER:
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.
QUE What is DML (Data Manipulation Language)?
ANS This language that enable user to access or manipulate data as organised by appropriate data model.
1) Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
2 ) Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.
QUES What is VDL (View Definition Language)?
ANS It specifies user views and their mappings to the conceptual schema.
QUES What is DML Compiler?
ANS It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
QUES What is Query evaluation engine?
ANS It executes low-level instruction generated by compiler.
QUES What is DDL Interpreter?
ANS It interprets DDL statements and record them in tables containing metadata.
QUES What is Record-at-a-time?
ANS 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.
QUES What is Set-at-a-time or Set-oriented?
ANS 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.
QUES What is Relational Algebra?
ANS 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.
QUES What is Relational Calculus?
ANS 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.
QUES How does Tuple-oriented relational calculus differ from domain-oriented relational calculus
ANS 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.
QUES What is normalization?
ANS It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties
1) Minimizing redundancy
2) Minimizing insertion, deletion and update anomalies.
QUES What is Functional Dependency?
ANS A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.
QUES When is a functional dependency F said to be minimal?
ANS 1) Every dependency in F has a single attribute for its right hand side.
2) We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.
3) We cannot remove any dependency from F and still have set of dependency that is equivalent to F.
QUES What is Multivalued dependency?
ANS Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
1 ) t3[x] = t4[X] = t1[X] = t2[X]
2) t3[Y] = t1[Y] and t4[Y] = t2[Y]
3) t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
QUES What is Lossless join property?
ANS It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
QUES What is 1 NF (Normal Form)?
ANS The domain of attribute must include only atomic (simple, indivisible) values.
QUES What is Fully Functional dependency?
ANS It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
QUES What is 2NF?
ANS A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
QUES What is 3NF?
ANS A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
1) X is a Super-key of R.
2) A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.
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