GWDA372

List the properties of a table.

A table has a name that is distinct from all other tables in the database.

There are no duplicate rows; each row is distinct.

Entries in columns are atomic. The table does not contain repeating groups or multi valued attributes.

Entries from columns are from the same domain based on their data type including:

number (numeric, integer, float, smallint,…)

character (string)

date

logical (true or false)

Operations combining different data types are disallowed.

Each attribute has a distinct name.

The sequence of columns is insignificant.

The sequence of rows is insignificant.

What two concepts of ER modeling based on?

Entities, defined as tables that hold specific information (data)

Relationships, defined as the associations or interactions between entities

Define the following terms:

Schema – A term referring to a database in MySQL

Host Language – The language that is used for database application programming

Data Sublanguage – A language or part of a language concerned only with database query and update and/or database definition

Unary Relation – one in which a relationship exists between occurrences of the same entity set

Foreign Key – an attribute in a table that references the primary key in another table OR it can be null

Virtual Relation – is defined from other preexisting relations

Connectivity – used to describe how well hardware or software devices can communicate with a range of other devicesConnectivity –

Composite Key – is composed of two or more attributes, but it must be minimal.

Linking Table – used for linking the two table or the fact tables

Provide three examples of the most popular relational databases used.

Microsoft SQL Server, Oracle Database, and MySQL 

What is the difference between centralized and distributed database systems?

Centralized systems puts all the information in a single location and users have the ability to access all the information in that one location. While the Distributed database system stores portions of the database in multiple computers within a network. Users have access to the portion of the database relevant to their tasks.

What is the difference between homogenous distributed database systems and heterogeneous distributed database systems?

Homogenous Distributed Database Systems is a network of two or more databases that reside on one or more machines. While Heterogeneous Distributed Database Systems might use different DDBMS software but has additional common software to support data exchange between sites.

What is data model?

The first step in the process of database design.

What is a high-level conceptual data model?

Provides concepts for presenting data in ways that are close tot he way people perceive data.

What is an entity? An attribute? A relationship?

Entity – represents a real-world object such as an employee or a project.

Attribute – Represents properties such as an employee’s name, address and birth date.

Relationship – Represents an association among entities.

List and briefly describe the common record-based logical data models.

Relational data models – represents data as relations, or tables.

network data models – represents data as record types.

hierarchical data models – represents data as a hierarchical tree structure.

Describe the purpose of a conceptual design.

A step sometimes considered to be a high-level and abstract design phase.

How is a conceptual design different from a logical design?

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What is an external model?

The end user’s view of the data.

What is a conceptual model?

Is the first model created based on the needs of various departments.

What is an internal model?

Consider a database as a collection of fixed-size records

Are closer to the physical level or file structure

Are a representation of the database as seen by the DBMS

Require the designer to match the conceptual model’s characteristics and constraints to those of the selected implementation model

Involve mapping the entities in the conceptual model to the tables in the relational model

What is a physical model?

The way the data is stored on disk.

Which model does the database administrator work with?

external models

Which model does the end user work with?

external model

What is logical data independence?

The ability to change the logical schema, without changing the external schema or user view

What is physical data independence?

Deals with hiding the details of the storage structure from user applications

What is a database management system (DBMS)?

Is a collection of programs that enables users to create and maintain databases and control all access to them.

What are the properties of a DBMS?

It is a representation of some aspect of the real word or a collection of data elements (facts) representing real world information.

A database of logical, coherent and internally consistent.

Designed, built and populated with data for a specific purpose.

Each data item is stores in a field.

A combination of fields makes up a table.

Provide three examples of a real-world database (e.g., the library contains a database of books).

Memberships to a gym.

Checking account at a bank.

Information in a hospital.

How is a DBMS distinguished from a file-based system?

A database system is referred to a self-describing because it not only contains the database itself, but also metadata which defines and describes the data and relationships between tables in the database. The separation of data and information about the data make a database system totally different.

What is a data independence and why is it important?

The insulation between the programs and data. It is important because the system data descriptions or data describing data are separated from the application programs.

What is the purpose of managing information?

To manipulate the data it houses so it can sort, match, link, aggregate, skip fields, calculate, arrange.

Discuss the uses of databases in a business environment.

Creating mailing lists.

Writing management reports

Generating lists of selected news stories

Identifying various client needs

What is metadata?

The system dat descriptions or data describing data.

Discuss each of the following terms:

• Data

A person, a place, an event, an action or any one of a number of things. A single fact is an element of data, or a data element.

• Field

A single piece of information.

• Record

One complete set of fields.

• File

A collection of records.

What is data redundancy?

A situation that occurs in a database when a field needs to be updated in more than one table.

Discuss the disadvantages of file-based systems.

Data Redundancy, Data isolation, Integrity problems, Security problems, and Concurrency access.

Explain the difference between data and information.

Data is raw, unorganized facts that need to be processed.

When data is processed, organized, structured or presented in a given context so as to make it useful, it is called information.

Use Figure 1.2 to answer the following questions:

In the table, how many records does the file contain?

7

How many fields are there per record?

5

What problem would you encounter if you wanted to produce a listing by city?

I wouldn’t be able to because the cities are combined with the rest of the address.

How would you solve this problem by altering the file?

I would separate the address information so the cities are in their own cell.