- What is an attribute?
It is a
particular property, which describes the entity.
- 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).
- What is degree of a Relation?
It is the number
of attribute of its relation schema.
- What is Relationship?
It is an
association among two or more entities.
- What is Relationship set?
The collection
(or set) of similar relationships.
- What is Relationship type?
Relationship
type defines a set of associations or a relationship set among a given set of entity types.
- What is degree of Relationship type?
It is the number
of entity type participating.
- What is DDL (Data Definition Language)?
A data base
schema is specifies by a set of definitions expressed by a special language
called DDL.
- What is VDL (View Definition Language)?
It specifies
user views and their mappings to the conceptual schema.
- What is SDL (Storage Definition Language)?
This language is
to specify the internal schema. This language may specify the mapping between
two schemas.
- 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.
- 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.
- What is DML Compiler?
It translates
DML statements in a query language into low-level instruction that the query
evaluation engine can understand.
- What is Query evaluation engine?
It executes
low-level instruction generated by compiler.
- What is DDL Interpreter?
It interprets
DDL statements and record them in tables containing metadata.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
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