Start Discovering Solved Questions and Your Course Assignments
TextBooks Included
Active Tutors
Asked Questions
Answered Questions
update anomaly this anomaly is occurred due to data redundancy redundant information makes updates more complex since for example varying the name of
data redundancy-a lot of information is being repeated in the relation for instance the information that mcs-014 is named ssad is repetitive address
domain constraintsdomain constraints are primarily formed for defining the logically correct values for an attribute of a relation the relation
foreign keys and nulllet us take the relation deptdept
before defines the second type of integrity constraint viz entity integrity we should be well-known with the concept of nullmostly null is intended
update or modify operation alters the existing values if these operations alter the value that is the foreign key also the only check need is the
the insertion of a tuple in the aim of reference does not cause any destruction though insertion of a tuple in the relation in which we has the
during the deletion of a tuple two cases can happendeletion of tuple in relation having the foreign key in this type of case simply delete the
it can be easily defined asthe database must not have any unmatched foreign key valuesthe term unmatched foreign key value means a foreign key value
primary keythe primary key is the candidate key that is selected by the database designer as the principal denotes of identifying entities within an
candidate key in a relation r a candidate key for r is a subset of the set of attributes of r which have the differnt two
a database is a set of data but is the data kept in a database trustworthy to answer that query we must first answer the question what is
relations create the database they must satisfy various properties like no duplicate tuples no ordering of tuples and atomic attributes etc relations
for every multivalued attribute a we make a new relation r that contains an attribute corresponding to plus the primary key attribute k of the
for every n-ary relationship type r where ngt2 we make a new table s to represent r we contain as foreign key attributes in s the primary keys of the
for each mn relationship type r we make a new table say s to represent r we also contain the primary key attributes of both the participating entity
for each 1 n relationship type r involving two entities e1 and e2 we recognize the entity type say e1 at the n-side of the relationship type r and
one-to-one relationshipfor every 11 relationship type r in the er diagram including two entities e1 and e2 we take one of entities say e1 preferably
conversion of entity setsi for every strong entity type e in the er diagram we make a
using the concepts defined previous we have identified that strong entities in college database are faculty student course and department this
aggregation one limitation of the e-r diagram is that they do not permit representation of relationships between relationships in such a case the
consider the entity type dependent related to employee entity which is used to keep track of the dependents of every employee the attributes of
entity types that do not have any key attribute and therefore cannot be identified independently are known as weak entity types a weak entity can be
the participation constraints shows whether the existence of an entity depends on its being associated to another entity by the relationship type
a relationship set is a set of relationships of the similar typefor example let consider the relationship among two entities sets course and student