Week 1 Revision Flashcards by Megan Briers

What were used before databases?

File systems, data stored in files, possibly separated with delimiters

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What were some disadvantages of file processing systems?

<ul>
<li>Data redundancy and Inconsistency</li>
<li>Difficulty in accessing data</li>
<li>Integrity problems, hard to check constraints</li>
<li>Can't guarantee atomicity of updates</li>
<li>Can't deal with concurrent access by multiple users easily</li>
<li>Hard to provide user access to some but not all data</li>
</ul>

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What is a database system?

A well controlled data repository with a collection of interrelated data and a set of programs to access the data

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What does the data model cover?

The data, the data relationships, the data semantics (shape and structure) and the constraints on the data

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What is described at the physical level of data abstraction?

How the record is stored

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What is described at the logical level of data abstraction?

How the data and relationships between data is stored in the database

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What is described at the view level of data abstraction?

Information about selected aspects of the data (certain groups)

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What is an instance?

The actual content of the database at a particular point of time

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What is physical data independence?

The ability to change the physical schema without affecting the logical schema

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How should the interfaces between various levels be defined?

So that a change inone part does not seriously influence the other parts

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What is logical data independence?

Ability to change the conceptual schema without having to modify the application programs which make use of them

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What are some examples of alterations in the conceptual schema?

Additional or deletion of entities, attributes and relationships

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Is logical data independence easier or harder to achieve than physical data independence?

Harder

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What are the steps in the database design methodology?

<ol>
  <li>Specification of requirements</li>
  <li>Choose data modelling style i.e. ER model</li>
  <li>Design data model</li>
<li>Choose database</li>
<li>Derive schema from data model</li>
<li>Populate database</li>
<li>Queries, updates, maintenance </li>
</ol>

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Give an example of a data model

ER diagram

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What are some benefits of using a data model?

<ul>
<li>Concise summary that you can present</li>
<li>Easy to understand</li>
<li>Hides irrelevant detail</li>
<li>Faster and easier to produce than code</li>
<li>Can go straight to code with some tools</li><li>
</li></ul>

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What are the two database languages?

Data Definition Lanuage

Data Manipulation Language

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Describe the Data Definition Language

DDL is the notation for defining the database scheme
Generates a set of table templates
Stores information about the data (metadata - integrity constraints, authorisation etc)
Commands such as CREATE, DROP, ALTER

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Describe the Data Manipulation Language

Language for accessing and manipulating the data
Two types : procedural and declarative
Commands such as SELECT, INSERT, DELETE

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What are the three functional components that a database system can be divided into?

<ol>
  <li>Storage Manager</li>
  <li>Query Processor Component</li>
  <li>Transaction Component</li>
</ol>

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What is the storage manager responsible for?

<ul>
<li>Interaction with the OS file manager</li>
<li>Efficient storing, retrieving and updating of data</li>
</ul>

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What is the query processor component responsible for?

<ul>
  <li>Interpreting and storing data definitions in the data dictionary</li>
  <li>Optimising queries</li>
  <li>Executing queries</li>
</ul>

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What is the transaction management component responsible for?

<ul>
<li>Helping with atomicity</li>
<li>Ensuring database stays in a consistent state</li>
<li>Controlling interaction between concurrent transactions</li>
</ul>

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What is the primary goal of a DBMS?

Store and retrieve database information that is both convenient and efficient?

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What kind of collections of data are databases used to store?

``` Ones that are

Highly valuable
Relatively large
Accessed by multiple users and applications at the same time

```

What are the two main modes where databases are used?

Online transaction processing
Data analytics

What is the major purpose of a database model?

To provide users with an abstract view of the data

What are the four data models?

```

Relational Model
Entity Relationship Model
Semi structured Data Model
Object based Data Model

```

What are the three main phases of the design process?

```

Conceptual design phase
Logical design
Physical design

```

What are the two things a database can be modelled as?

A collection of entities and the RELATIONSHIP between those entities

What is an entity?

An object that exists and is distinguishable from other objects

What are attributes?

Descriptive properties/characteristics of the object

What is an entity set?

Set of entities of the same type that share the same set of attributes

What are the five types of attributes?

```

Simple
Composite
Single-valued
Multi-valued
Derived

```

What is a simple attribute?

An attribute that is made up of a single component part

What is a composite attribute?

An attribute that is made up of multiple component parts e.g. address

What is a single valued attribute?

An attribute that can only have one value per entity

What is an example of a single valued attribute?

Date of birth, salary

What is a multi valued attribute?

An attribute that can have more than one value per entity

What is an example of a multi valued attribute?

Phone number

What is a derived attribute?

An attribute that is computed from other attributes

What is an example of a derived attribute?

Age from date of birth and current date

What is a relationship?

An association that exists between entities that is uniquely identifiable

What is a relationship set?

Set of relationships between one or more entity sets

What are the two cardinalities of relationship sets?

Binary relationships | N-ary relationships

What do multiplicity constraints cover?

Number of times an entity can or must take part in a particular type of relationship

Describe Participation

The MINIMUM number of times an entity must take part in the relationship set

Describe Cardinality

The MAXIMUM number of times an entity can take part in a relationship set

What is total participation?

An entity MUST take part in the relationship set

What is partial participation?

An entity may or may not take part in the relationship set

What is the cardinality of a one to one relationship?

What is the cardinality of the left set in a one to many relationship?

Greater than 1

What is a candidate key?

The minimal set of attributes that are needed to uniquely identify each entity

What is a primary key?

The candidate key chosen to uniquely identify each entity

What is a weak entity set?

An entity set with no candidate keys

What do weak entity sets depend on?

The existence of an identifying entity set

What are the conditions for relationships between weak entity sets and identifying entity sets?

WES must have total participation in relationship with identifying set
Must be one to many relationship from identifying set to weak entity set

What is the discriminator of a weak entity set?

Set of attributes that distinguishes it among all entities of a weak entity set

What is the primary key of a weak entity set formed by?

The primary key of the identifying entity set and the weak entity set's discriminator

What key concept is not formally represented in an ER diagram?

Foreign Keys

How are composite attributes represented in an ER diagram?

Identation

How are derived attributes represented in an ER diagram?

Parentheses

How are multi-valued attributes represented in an ER diagram?

Braces

How is total participation represented in an ER diagram?

Double line

How is a cardinality of one represented in an ER diagram?

Arrow

How are discriminators represented in an ER diagram?

Dashed line underline

How are relationships to identifying entity sets represented in an ER diagram?

Double outline