Databases Reference
In-Depth Information
Summary
26
Problems with nondatabase approaches to data management include redundancy, difficulties accessing
related data, limited security features, limited data sharing features, and potential size limitations.
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An entity is a person, place, object, event, or idea for which you want to store and process data. An attribute,
field, or column is a characteristic or property of an entity. A relationship is an association between entities.
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A one-to-many relationship between two entities exists when each occurrence of the first entity is related to
many occurrences of the second entity and each occurrence of the second entity is related to only one occur-
rence of the first entity.
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A database is a structure that can store information about multiple types of entities, the attributes of the enti-
ties, and the relationships among the entities.
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Premiere Products is an organization whose requirements include information about the following entities:
reps, customers, parts, orders, and order lines.
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An entity-relationship (E-R) diagram represents a database visually by using a rectangle for each entity that
includes the entity's name above the rectangle and the entity's columns inside the rectangle, using a line to
connect two entities that have a relationship, and placing a dot at the end of a line to indicate the “many” part
of a one-to-many relationship.
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A database management system (DBMS) is a program, or a collection of programs, through which users inter-
act with a database. DBMSs let you create forms and reports quickly and easily, as well as obtain answers
to questions about the data stored in a database.
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Database processing offers the following advantages: getting more information from the same amount of data,
sharing data, balancing conflicting requirements, controlling redundancy, facilitating consistency, improving
integrity, expanding security, increasing productivity, and providing data independence. The disadvantages of
database processing include the following: larger file size, increased complexity, greater impact of failure, and
more difficult recovery.
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Henry Books is a company whose requirements include information about the following entities: branches,
publishers, authors, books, inventory, and author sequence.
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Alexamara Marina Group is a company whose requirements include information about the following entities:
marinas, owners, marina slips, service categories, and service requests.
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attribute
column
data file
data independence
database
database administration (DBA)
database administrator
database design
database management system (DBMS)
entity
entity-relationship (E-R) diagram
field
form
integrity
integrity constraint
one-to-many relationship
redundancy
relationship
security
1.
What is redundancy? What problems are associated with redundancy?
2.
Besides redundancy, what other problems are associated with the nondatabase approach to processing data?
3.
What is an entity? An attribute?
4.
What is a relationship? A one-to-many relationship?
5.
What is a database?
6.
How do you create a one-to-many relationship in a database system?
