CHAPTER 9
DATABASE MANAGEMENT SYSTEMS
1. REVIEW QUESTIONS
3. The primary difference between the network and hierarchical models is in the
4.
6. One level is the schema, which is the conceptual view of the data. The
schema describes the entire database, and it represents the database
logically. The second level is the internal view which is the physical
8. Logically related tables need to be physically connected to achieve the
associations described in the data model. This is accomplished by
9.The data dictionary describes every data element in the database. The
data dictionary enables all users (and programmers) to share a common
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10. An organization has three diverse operating units: tractors, sewing
machines, and computer chips. These units have different customers,
11. An entity is anything about which the organization wishes to capture data.
Entities may be physical, such as “Inventory”, “Customer”, or “Employee”.
12. The XYZ company is a geographically distributed organization with several
13. (1:0,1) Every occurrence (record) is for one entity (Employee), there is a
possibility of zero or one occurrence in the related entity (Company Car).
(1:1) Describes a situation in which each record in one entity is always
associated with one (and only one) record in the associated entity. For
14. The term association pertains to the nature of the relationship between two
entities. This is represented by a verb such as shipped, requests, or receives.
15. In a many-to-many association, a link table with a combined (composite) key
17. a. Restrict—Extracts rows that satisfy the given condition from a specified
table and places these rows into a new table.
18. A table normalized to 3NF meets the following conditions:
2. All nonkey attributes are independent of the other nonkey attributes.
In other words, the primary key of a table wholly and uniquely defines
19. The user may restrict the fields of data to view with the SELECT
command. Further, the user may restrict the rows or records of data to be
20. A data model is the blueprint for creating the physical database. Database
21. The deletion anomaly may cause records to be deleted unintentionally and
may occur for some time before the problem is noticed. A deletion anomaly
occurs when an item in one file is legitimately deleted. The problem occurs
22. A user view is the set of data that a particular user sees. Examples of user
23. User views derive from underlying database tables. Simple views may be
24. Valid entities meet the three conditions below:
25. Because attributes are the logical and relevant characteristics of an entity, they
2.
3.
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4. DISCUSSION QUESTIONS
developed with data and program dependency. Typically, these
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2. If your university were to use different databases for the registrar, library,
parking, food services, and computing services, then the number of forms you
would have to fill out, if any of your personal data changes, would be plentiful.
For example, if you were to move during the semester to a different apartment,
the university should be notified. In this situation, a couple of things could
happen. You could be required to go to each service individually and fill out an
3. Under the database concept, the data becomes centrally stored with many
different users accessing the database. However, each user should not have
access to the whole database. Under the traditional data management
4. User views are derived database tables. A single table may contribute data to
5. Tables that are logically related in the data model need to be physically linked.
The degree of association between the tables (i.e., 1:1, 1:M, or M:M)
determines how the linking occurs. The key-assignment rules for linking tables
are discussed below:
6. The entity relationship (ER) diagram is the graphical representation
technique used to depict a data model. Each entity in an ER diagram is
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7. SQL allows users to retrieve data from many different files without the
assistance of programmer professionals. Thus, if the user has access to data
8. The data was not centrally stored for many different applications to use in
the traditional data management environment; therefore, a database
administrator was not needed. Because it is centrally stored and shared by
many users in a database environment, the need arose for an individual to
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9. The system programmer’s program should not have access to the data, except
perhaps temporarily to test the programs. The database administrator controls
10. Neither table can donate an embedded key to the other, because both are on
11. Tables that are not normalized contain anomalies which require excessive
updates to tables, prevent data from being stored properly, and may cause
12. A database lockout prevents multiple users from accessing the same table
simultaneously and making changes to data values while they are temporarily
13. Database concurrency controls ensure the completeness and accuracy of a
distributed database at remote sites where the same beginning data balances
14. Database accounting systems are transaction-based rather than
account-based. The focus is on capturing important details of transactions that
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15. Where a true 1:1 association exists between tables, either (or both) primary
keys may be embedded as foreign keys in the related table. On the other hand,
when the lower cardinality value is zero (1:0,1), a more efficient table structure
can be achieved by placing the 1-side (1:) table’s primary key in the
zero-or-one (:0,1) table as a foreign key. Assume that a company has 1000
employees, but only 100 of them are sales staff. Also assume that each sales
16. The insertion and update anomalies would create record keeping and
operational problems for the firm. However, flawed databases design that
prevents the insertion of records, or requires the user to perform excessive
updates, would attract attention quickly. The presence of the deletion anomaly
17. The organization’s business rules directly impact the structure of the database
tables. If the database is to function properly, its designers need to understand
the organization’s business rules, as well as the specific needs of individual
users. For example:
1. When an organization decides
to purchase the same items of inventory from different suppliers, the
2. When a the company
purchases all items of a certain type from only one supplier, the
3. A policy that a separate
receiving report is prepared for the receipt of goods specified on a single
18. The partitioned approach works best for organizations that require minimal
data sharing among users at remote sites. To the extent that remote users
share common data, the problems associated with the centralized approach
19. To achieve data currency, simultaneous access to individual data elements or
records by multiple users needs to be prevented. The solution to this problem
is a database lockout, which is a software control that prevents multiple
20. The primary justification for a replicated database is to support read-only
queries in situations involving a high degree of data sharing, but no primary
user exists. With data replicated at every site, data access for query purposes
is ensured, and lockouts and delays due to network traffic are minimized. A
potential problem arises, however, when replicated databases need to be
6.
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