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DBMS > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

The basic concept that the ER model represents is an ____

A

entity

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2
Q

Entity

A

Thing or object in the real world with an independent existence
- Can be an object with a physical existence

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3
Q

Attributes

A

properties that describe entities

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4
Q

Composite Attributes

A

represent more basic attributes with independent meanings
- Ex: Address can be divided into Street, Address, City, State, Zip
- Can form a hierarchy

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5
Q

Atomic Attributes (simple)

A

Are not divisible

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6
Q

Single-Valued Attributes

A

Single-Valued attributes have a single value per entity
- Ex: age

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7
Q

Multivalued Attributes

A

Multivalued attributes can have multiple values per entity
- Ex: one person can have many college degrees
- can have lower and upper bounds

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8
Q

Derived Attributes

A

Derived Attributes are derivable from a stored attribute
- Age = Derives
- Date of birth = Stored

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9
Q

Null values

A

In some cases, a particular entity will not have a value for an attribute
- Ex: some addresses don’t have an apartment number

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10
Q

Complex Attributes

A
  • Arbitrary nesting by grouping components of composite attributes
  • Ex: a person can have more than one residence and each residence can have a single address and multiple phones, an attribute Address_phone for a person can be specified - phone and address are composite attributes
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11
Q

Entity type

A

defines a collection of entities that have similar attributes
- Each type of entity in the database is defined by its name and attributes
- Describes the schema or intension for a set of entities that share the same structure

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12
Q

Entity Set or Entity Collection

A

The collection of all entities of a particular entity type in the database at any point
- The extension of the entity type - the collection of entities of a particular entity type is grouped into an entity set

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13
Q

Attributes of an Entity Type

A
  • Key or Uniqueness constraint - identifying value
  • Specifying that an attribute is a key of an entity type means that the preceding uniqueness property must hold for every entity set of the entity type.
  • Entity types can have more than one key attribute
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14
Q

Value Sets (Domains) of Attributes

A
  • Specifies the set of values that may be assigned to that attribute for each individual entity
  • Ex: If the range of ages allowed for employees is between 16 and 70, we can specify the value set of the Age attribute of EMPLOYEE to be the set integer numbers between 16 and 70
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15
Q

In ER diagrams, relationship types are displayed as ___ boxes

A

diamond-shaped

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16
Q

Relationships

A
  • The degree of a relationship type is the number of participating entity types
17
Q

Role name

A

Signifies the role that a participating entity from the entity type plays in each relationship instance, and it helps to explain what the relationship means
- Recursive relationships
- Self-referencing relationships

18
Q

Constraints on Binary Relationship Types

A
  • Relationship types usually have certain constraints that limit the possible combinations of entities that may participate in the corresponding relationship set
  • Participation Constraint
  • Minimum cardinality constraint
  • Total participation (existence dependency)
19
Q

For a 1:N relationship type, a relationship attribute can be migrated only to the entity type on the ____ of the relationship

A

N-side

20
Q

Weak Entity Types

A

Entity types that do not have key attributes of their own are called weak entity types
- Strong entity types are the opposite
- A weak entity type normally has a partial key, which is the attribute that can uniquely identify weak entities that are related to the same owner entity.

21
Q

What is the Relational Model?

A
  • A database of relations
  • Each relation resembles a table of values or a flat file of records
22
Q

Formal relational model terminology

A

Row - tuple
Column header - attribute
Table - relation
The data describing the types of values that can appear in each column by a domain of possible values

23
Q

Domains

A

A domain is a set of atomic values
- Assigning data types is specifying a domain

24
Q

Atomic

A

Each value in the domain is indivisible as far as the formal relational model is concerned

25
Q

Attributes

A

A relation schema2 R, denoted by R(A1, A2, …, An) is made up of a relation name R and a list of attributes, A1, A2, …, An
- Each attribute, Ai, is the name of a role played by some domain, D, in the relation schema, R

26
Q

The degree of a relation is the

A

number of attributes n of its relation schema

27
Q

Attributes and Terms

A

A relation of degree seven would contain seven attributes
- A relation of a relation schema is a set of n-tuples
- Each n-tuple t is an ordered list of n values

28
Q

Cardinality

A

Total number of values in a domain
- We can define a relation as the mathematical relation of degree n on the domains dom(A1), dom(A2), dom(An) which is a subset of the Cartesian product of the domains that define R

29
Q

Current relation state

A

reflects only the valid tuples that represent a particular state of the real world

30
Q

Roles

A

It is possible for multiple attributes to have the same domain
- The attribute names indicate different roles (interpretations_ for the domain

31
Q

Relation vs a file or table

A

Relation is a defined set of tuples that have no particular order
- File records are physically stored on memory so there is always an order

32
Q

Relational Model Notation

A
  • A relation schema R of degree n is denotes by R(A1, A2, An)
  • The uppercase letters Q, R, S denote relation names
  • The lowercase letters q,r,s denote relation states
  • The letters t, u, v denote tuples
33
Q

Relational Model Constraints

A

Inherent model-based constrains (implicit constraints) - these are existing as permanent in the model or as a characteristic attribute
- Schema-based constraints (explicit constraints) - constraints that can be directly expressed in the schemas of the data model, typically by specifying them in the DDL (data definition language)
- Application-based (semantic constraints or business rules) - Constraints that cannot be directly expressed in the schemas of the data model

34
Q

Data Dependencies (functional and multivalued dependencies)

A

Used mainly for testing the “goodness: of the design of a relational database and are utilized in a process called normalization

35
Q

Relational database schema

A

S is a set of relation schemas and a set of integrity constraints IC

DBMS (2 decks)

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