inf sys

Question 1

multivalued attribute

Answer 1

e.g. skills of person since football, hockey = 2 things you you can have multiple things in one attribute skills

Question 2

what are the different cardinality ratios

Answer 2

1:N M:N (an employee

can work on several projects and a project can have several employees) 1:1 (one manager 1 department)

Question 3

what are the participation constraints

Answer 3

total and partial participation (2 lines vs 1 line)

Question 4

if you have a relation attribute, you can move it to the entities with the most relations to one of the other entity.

Answer 4

yup

Question 5

For M:N relationship types, some attributes may be determined by the combination of
participating entities in a relationship instance, not by any single entity. Such attributes must be specified as:

Answer 5

relationship attributes

Question 6

weak entity types are:

Answer 6

antities without a key attribute, relying on another entity for its identifier

Question 7

A weak entity type normally has a partial key, which is the set of attributes that can
uniquely identify weak entities that are related to the same owner entity.

Answer 7

yup

Question 8

weak entities in ER hebben

Answer 8

dubbele lijnen

Question 9

composite attributes

Answer 9

consist out of multiple things

Question 10

Derived attribute

Answer 10

Derived attributes are the attributes that do not exist in the physical database, but their values are derived from other attributes present in the database.

Question 11

what is a key?

Answer 11

an attribute / attributes that uniquely identify an entity

Question 12

what is the difference between ER and EER? (the enhanced)

Answer 12

subclasses, superclasses and inheritance specialisation is adding subclasses whereas generalization is using superclasses

Question 13

1. How do we define the members of a subclass?

Answer 13

 Predicate-defined or condition-defined: based on some
predicate/attribute value.
 Attribute-defined: based on an attribute of a superclass
 User-defined: membership is defined by the user on an
entity-by-entity basis

Question 14

How many subclasses may an entity belong to?

Answer 14

 Disjointness Constraint - disjouint or overlapping

 Completeness Constraint

Question 15

specializations can thus be defined by

Answer 15

an attribute, meaning that based on that attribute, the entity will be specifying what subclass it will become.

Question 16

what is the hierarchy constraint?

Answer 16

each subclass can maximally be part of one superclasse (meaning the graph has a tree structure). or it doesn’t have this constraint and then the graph has lattices.

Question 17

what are categories / union types?

Answer 17

see a single super/subclass relation that can have different types. Basically it is a subclass the might inherit from any of its super classes (literally a union) since the superclasses are usually of different types. for instance OWNER can be a bank or a person.

Question 18

give the relational algebra functions

Answer 18

sigma(R) = select from R where 
pi(R) = select attributes name1 and nam2 from R -> removes duplicate tuples
rho s  (R) renames R to s and the attributes to name1 and name2 (rename the attributes of a relation or the relation's name or both).

Question 19

what are the relational algebra operations from set theory?

Answer 19

UNION (  ), INTERSECTION (  ), DIFFERENCE (or MINUS, – )

and CARTESIAN PRODUCT ( x )

Question 20

what is the difference between inner join, left join and cross join

Answer 20

bij inner join match je de eerst genoemde select met de join. dus de table zijn eerste kolom heeft de eerst genoemde select. bij left join clause selects data starting from the left table (artists) and matching rows in the right table (albums) based on the join condition dus hier selecteer je de albums ipv de artiesten. als je er een where aan toevoegd dan kan je bijvoorbeeld selecteren alle artiesten die geen album hebben. cross join just creates the cartesian product.