AIS Ch. 8

Give three examples that illustrate how cardinality reflects an organization's underlying business rules.

1) When an organization decides to purchases the same items of inventory from different suppliers, the cardinality between the Supplier and Inventory tables is M:M. 2) When a the company purchases all items of a certain type from only one supplier, the cardinality between Supplier and Inventory tables is 1:M respectively. 3) A policy that a separate receiving report is prepared for the receipt of goods specified on a single purchase order will result in a 1:1 cardinality between the receiving report and purchase order tables. If, however, multiple purchase orders are combined on a single receiving report then the cardinality between these tables will be 1: M respectively.

What is a hashing structure? What are the advantage(s) and disadvantage(s) associated with it?

A hashing structure employs an algorithm that converts the primary key of a record directly into a storage address. Hashing eliminates the need for a separate index. By calculating the address, rather than reading it from an index, records can be retrieved more quickly. The principal advantage of hashing is access speed. The hashing technique has two disadvantages. It does not use storage space efficiently. The storage location chosen for a record is a mathematical function of its primary key value. The algorithm will never select some disk locations because they do not correspond to legitimate key values. Different record keys may generate the same (or similar) residual, which translates to the same address. This is called a collision because two records cannot be stored at the same location.

What is a partial dependency?

A partial dependency occurs when one or more nonkey attributes are dependent on (defined by) only part of the primary key, rather than the whole key. This can occur only in tables that have composite (two or more attribute) primary keys.

Discuss the two fundamental components of data structures.

Organization refers to the way records are physically arranged on the secondary storage device. This may be either sequential or random. The records in sequential files are stored in contiguous locations that occupy a specified area of disk space. Records in random files are stored without regard for their physical relationship to other records in the same file. Random files may have records distributed throughout a disk. The access method is the technique used to locate records and to navigate through the database or file. While several specific techniques are used, in general, they can be classified as either direct access or sequential access methods.

How can a poorly designed database result in unintentional loss of critical records?

The deletion anomaly may cause data to be deleted unintentionally from incorrectly normalized tables. In such situations, records that are legitimately deleted from the table may result in the deletion of other data not intended for deletion.

Give an example of the insertion anomaly.

The insertion anomaly occurs when certain types of new records can not be added. For example, if the primary key for the vendor file is PART NUMBER, a new vendor cannot be added until a purchase is made.

Explain the three types of anomalies associated with database tables that have not been normalized.

The update anomaly is the result of data redundancy. If a data element is stored in more than one place, it must be updated in all places. If this does not happen, the data are inconsistent. The insertion anomaly occurs when too much data is stored together-when vendor information is only stored with specific inventory items. Until items are purchased from a given vendor, the vendor cannot be added to the database. The deletion anomaly is the opposite of the insertion anomaly-if a vendor supplies only one item, and the firm discontinues that item, all information on the vendor is lost when vendor information is only stored with specific inventory items.

What is the update anomaly?

The update anomaly results from data redundancy in an unnormalized table. The data attributes pertaining to particular entity (for example: Vendor Name, Address, and Tele Num) are repeated in every record in every record pertaining to the vendor. Any change in the supplier's name, address, or telephone number must then be made to each of these records. This causes an update problem that results in excessive overhead costs.

What are the key control implications of the absence of database normalization?

When considering the quality of the data in a database, accountants should be aware of the outcomes of typical anomalies. The update anomaly can yield conflicting data in the database. The insertion anomaly can result in unrecorded transactions. The deletion anomaly can cause loss of accounting information and destruction of the audit trail.

Explain the following three types of pointers: physical address pointer, relative address pointer, and logical key pointer.

A physical address pointer contains the actual disk storage location (cylinder, surface, and record number) needed by the disk controller. This approach allows the system to access the record directly without obtaining further information. A relative address pointer contains the relative position of a record in the file. This address (i.e., the 200th record on the file) must be further manipulated to convert it to the actual physical address. The conversion software determines this by using the physical address of the beginning of the file, the length of each record in the file, and the relative address of the record being sought. A logical key pointer contains the primary key of the related record. This key value is then converted into the record's physical address by a hashing algorithm.

When is a table in third normal form (3NF)?

A table is in third normal form when it meets the two conditions below: 1. All nonkey (data) attributes in the table are dependent on (defined by) the primary key. 2. All nonkey attributes are independent of the other nonkey attributes.

What is a transitive dependency?

A transitive dependency occurs in a table where nonkey attributes are dependent on another nonkey attribute and independent of the table's primary key.

Contrast embedded audit modules with generalized audit software.

Both techniques permit auditors to access, organize, and select data in support of the substantive phase of the audit. The embedded audit module (EAM) technique embeds special audit modules into applications. The EAM captures specific transactions for auditor review. EAMs reduce operational efficiency and are not appropriate for environments with a high level of program maintenance. Generalized audit software (GAS) permits auditors to electronically access audit files and to perform a variety of audit procedures. For example the GAS can recalculate, stratify, compare, format, and print the contents of files. The EAM is an internal program that is designed and programmed into the application. The GAS is an external package that does not affect operational efficiency of the program. GASs are easy to use, require little IT background on the part of the user, are hardware independent, can be used without the assistance of computer service employees, and are not application-specific. On the other hand, EAMs are programmed into a specific application by computer service professionals.

What is repeating group data?

Each unique primary key value is associated with multiple values for nonkey attributes.