DBMS PART 2

21. What is an attribute? It is a particular property, which describes the entity.

22. What is a Relation Schema and a Relation? A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).

23. What is degree of a Relation? It is the number of attribute of its relation schema.

24. What is Relationship? It is an association among two or more entities.

25. What is Relationship set? The collection (or set) of similar relationships.

26. What is Relationship type? Relationship type defines a set of associations or a relationship set among a given set of entity types.

27. What is degree of Relationship type? It is the number of entity type participating.

25. What is DDL (Data Definition Language)? A data base schema is specifies by a set of definitions expressed by a special language called DDL.

26. What is VDL (View Definition Language)? It specifies user views and their mappings to the conceptual schema.

27. What is SDL (Storage Definition Language)? This language is to specify the internal schema. This language may specify the mapping between two schemas.

28. What is Data Storage - Definition Language? 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.

29. What is DML (Data Manipulation Language)? This language that enable user to access or manipulate data as organised by appropriate data model. Ø Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data. Ø Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.

31. What is DML Compiler? It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.

32. What is Query evaluation engine? It executes low-level instruction generated by compiler.

33. What is DDL Interpreter? It interprets DDL statements and record them in tables containing metadata.

34. What is Record-at-a-time? 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.

35. What is Set-at-a-time or Set-oriented? 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.

36. What is Relational Algebra? 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.

37. What is Relational Calculus? 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.

38. How does Tuple-oriented relational calculus differ from domain-oriented relational calculus 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.

39. What is normalization? It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties Ø Minimizing redundancy Ø Minimizing insertion, deletion and update anomalies.

40. What is Functional Dependency? 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.

41. When is a functional dependency F said to be minimal? Ø Every dependency in F has a single attribute for its right hand side. Ø 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. Ø We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

42. What is Multivalued dependency? 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 Ø t3 = t4[X] = t1[X] = t2[X] Ø t3[Y] = t1[Y] and t4[Y] = t2[Y] Ø t3[Z] = t2[Z] and t4[Z] = t1[Z] where [Z = (R-(X U Y)) ]

43. What is Lossless join property? It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.

44. What is 1 NF (Normal Form)? The domain of attribute must include only atomic (simple, indivisible) values.

45. What is Fully Functional dependency? 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.

46. What is 2NF? 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.

47. What is 3NF? A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true Ø X is a Super-key of R. Ø A is a prime attribute of R. In other words, if every non prime attribute is non-transitively dependent on primary key.

48. What is BCNF (Boyce-Codd Normal Form)? A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.

49. What is 4NF? A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true Ø X is subset or equal to (or) XY = R. Ø X is a super key.

50. What is 5NF? A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true Ø Ri = R for some i. Ø The join dependency is implied by the set of FD, over R in which the left side is key of R.