Podcast
Questions and Answers
A ______ is an entity without a key attribute.
A ______ is an entity without a key attribute.
Weak Entity
In ER diagrams, ______ are displayed in ovals.
In ER diagrams, ______ are displayed in ovals.
Attributes
A ______ attribute is displayed in a double oval.
A ______ attribute is displayed in a double oval.
Multivalued
Each ______ attribute is underlined in ER diagrams.
Each ______ attribute is underlined in ER diagrams.
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A ______ attribute is displayed in a dotted oval.
A ______ attribute is displayed in a dotted oval.
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The degree of a ______ type is the number of participating entities in a relationship.
The degree of a ______ type is the number of participating entities in a relationship.
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A ______ relationship exists between the instances of the same entity type.
A ______ relationship exists between the instances of the same entity type.
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A ______ relationship exists among the instances of three entity types.
A ______ relationship exists among the instances of three entity types.
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An _______________ server runs application programs and stores business rules (constraints).
An _______________ server runs application programs and stores business rules (constraints).
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Entities are specific persons, places, events, objects in the user environment about which the user needs to keep _______________.
Entities are specific persons, places, events, objects in the user environment about which the user needs to keep _______________.
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Attributes are properties used to describe an _______________.
Attributes are properties used to describe an _______________.
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A specific entity will have a value for each of its _______________.
A specific entity will have a value for each of its _______________.
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Each attribute has a _______________ type associated with it – e.g. integer, string, …
Each attribute has a _______________ type associated with it – e.g. integer, string, …
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A _______________ relates two or more distinct entities with a specific meaning.
A _______________ relates two or more distinct entities with a specific meaning.
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The _______________ server accepts requests from the client, processes it, and sends DB queries and commands to the DB server.
The _______________ server accepts requests from the client, processes it, and sends DB queries and commands to the DB server.
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Clients contain _______________ interfaces and Web browsers.
Clients contain _______________ interfaces and Web browsers.
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EMPLOYEE John Smith works on the ______ PROJECT, or EMPLOYEE Franklin Wong manages the Research ______.
EMPLOYEE John Smith works on the ______ PROJECT, or EMPLOYEE Franklin Wong manages the Research ______.
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Each attribute has a single ______ value. For example, SSN or Sex.
Each attribute has a single ______ value. For example, SSN or Sex.
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The attribute may be composed of several ______ components. For example, Address(Apt#, House#, Street, City, State, ZipCode, Country).
The attribute may be composed of several ______ components. For example, Address(Apt#, House#, Street, City, State, ZipCode, Country).
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An attribute that may have ______ values. For example, Color of a CAR – {Black, White}.
An attribute that may have ______ values. For example, Color of a CAR – {Black, White}.
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An attribute that have only a single ______. For example, SSN or Sex.
An attribute that have only a single ______. For example, SSN or Sex.
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An Attribute with a value ______ by the user to be stored in the DB. For example, BirthDate, Salary, Bonus.
An Attribute with a value ______ by the user to be stored in the DB. For example, BirthDate, Salary, Bonus.
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An attribute with a value ______ from other stored attributes and no need to ask user for it. For example, from BirthDate attribute we derive the Age.
An attribute with a value ______ from other stored attributes and no need to ask user for it. For example, from BirthDate attribute we derive the Age.
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Study Notes
Types of Attributes
- Simple attribute: has a single atomic value, e.g. SSN or Sex
- Composite attribute: composed of several components, e.g. Address (Apt#, House#, Street, City, State, ZipCode, Country) or Name (FirstName, MiddleName, LastName)
- Composition may form a hierarchy where some components are themselves composite
Types of Attributes (2)
- Single-valued attribute: has only a single value, e.g. SSN or Sex
- Multi-valued attribute: may have multiple values, e.g. Color of a CAR – {Black, White} or PreviousDegrees of a STUDENT—{BSc, MSc, PhD}
Types of Attributes (3)
- Stored attribute: an attribute with a value entered by the user to be stored in the DB, e.g. BirthDate, Salary, Bonus
- Derived attribute: an attribute with a value derived from other stored attributes, e.g. Age from BirthDate or NetSalary from Salary and Bonus
Types of Attributes (4)
- Complex attribute: considered composite and multivalued at the same time, e.g. PhoneNumber (country code, gov.code, phone) with multiple values
Entities and Attributes
- Entity: a specific person, place, event, or object in the user environment, e.g. EMPLOYEE, Office, Task, Conference
- Attribute: a property used to describe an entity, e.g. EMPLOYEE attributes: Name, SSN, Address, Sex, BirthDate
- Each attribute has a data type associated with it, e.g. integer, string, …
Relationships
- A relationship relates two or more distinct entities with a specific meaning, e.g. EMPLOYEE John Smith works on the ProductX PROJECT, or EMPLOYEE Franklin Wong manages the Research DEPARTMENT
- Degree of a relationship type: the number of participating entities in a relationship, e.g. Unary, Binary, Ternary
Types of Relationships
- Unary relationship: a relationship between instances of the same entity type, e.g. a person lives with another
- Binary relationship: a relationship between instances of two entity types, e.g. EMPLOYEE and DEPARTMENT
- Ternary relationship: a relationship among instances of three entity types, e.g. EMPLOYEE, PROJECT, and DEPARTMENT
ER Diagrams
- Entities: displayed in rectangular boxes, with weak entities displayed in double rectangular boxes
- Attributes: displayed in ovals, with each attribute connected to its entity type
- Components of composite attributes: connected to the oval representing the composite attribute
- Key attributes: underlined
- Multivalued attributes: displayed in double ovals
- Derived attributes: displayed in dotted ovals
Three-Tier and n-Tier Architectures
- Three-Tier Architecture: improves DB security by checking a client's credentials before forwarding a request to the DB server
- N-Tier Architecture: divides the layers between the user and the stored data further into finer components
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Description
This quiz covers the basics of three-tier architecture, including the role of application servers, web servers, and database servers in processing client requests and enforcing security constraints.
