80 terms

System Analysis and design Chapter 9

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1:1
A type of entity relationship. A one-to-one relationship, abbreviated 1:1, exists when exactly one of the second entity occurs for each instance of the first entity.
1:M
A type of entity relationship. A one-to-many relationship, abbreviated 1:M, exists when one occurrence of the first entity can be related to many occurrences of the second entity, but each occurrence of the second entity can be associated with only one occurrence of the first entity.
abbreviation code
Alphabetic abbreviation. For example, standard state codes include NY for New York, ME for Maine, and MN for Minnesota.
absolute date
The total number of days from some specific base date. To calculate the number of days between two absolute dates, subtract one date from the other. For example, using a base date of January 1, 1900, September 27, 2012, has an absolute date value of 41179 and July 13, 2011, has an absolute date of 40737. If the earlier date value is subtracted from the later one, the result is 442 days
action code
Indicates what action is to be taken with an associated item. For example, a student records program might prompt a user to enter or click an action code such as D (to display the student's record), A (to add a record), and X (to exit the program).
alphabetic code
Uses alphabet letters to distinguish one item from another based on a category, an abbreviation, or an easy-to-remember value, called a mnemonic code.
ASCii
Stands for American Standard Code for Information Interchange, a data storage coding method used on most personal computers and workstations.
associative entity
An entity that has its own set of attributes and characteristics. Associative entities are used to link between many-to-many (M:N) relationships.
audit fields
Special fields within data records to provide additional control or security information. Typical audit fields include the date the record was created or modified, the name of the user who performed the action, and the number of times the record has been accessed.
audit log files
Record details of all accesses and changes to a file or database and can be used to recover changes made since the last backup.
backup
The process of saving a series of file or data copies to be retained for a specified period of time. Data can be backed up continuously, or at prescribed intervals.
binary storage format
A format that offers efficient storage of numeric data. For example, when numeric data types are specified using Microsoft Access, there are a variety of storage formats choices, including integer and long integer, among others.
bit
The smallest unit of data is one binary digit.
block sequence code
Cipher that uses blocks of numbers for different classifications.
byte
A group of eight bits is called a byte, or a character. A set of bytes forms a field, which is an individual fact about a person, place, thing, or event.
candidate key
Sometimes it is possible to have a choice of fields or field combinations to use as the primary key. Any field that could serve as a primary key is called a candidate key.
cardinality notation
Code that shows relationships between entities.
category code
Cipher that identifies a group of related items. For example, a local department store may use a two-character category code to identify the department in which a product is sold.
character
A group of eight bits is called a character, or a byte. A set of bytes forms a field, which is an individual fact about a person, place, thing, or event.
cipher code
Use of a keyword to encode a number. A retail store, for example, may use a 10-letter word, such as CAMPGROUND, to code wholesale prices, where the letter C represents 1, A represents 2, and so on. Thus, the code, GRAND, would indicate that the store paid $562.90 for the item.
clicks to close
The average number of page views to accomplish a purchase or obtain desired information.
clickstream storage
Recording web visitor behavior and traffic trends for later data mining use.
code
A set of letters or numbers that represents a data item. Codes can be used to simplify output, input, and data formats
combination key
A type of data validation check that is performed on two or more fields to ensure that they are consistent or reasonable when considered together. Even though all the fields involved in a combination check might pass their individual validation checks, the combination of the field values might be inconsistent or unreasonable.
common field
An attribute that appears in more than one entity. Common fields can be used to link entities in various types of relationships.
composite key
Sometimes it is necessary for a primary key to consist of a combination of fields. In that case, the primary key is called a combination key, composite key, concatenated key, or multivalued key.
crow's foot notation
A type of cardinality notation. It is called crow's foot notation because of the shapes, which include circles, bars, and symbols, that indicate various possibilities. A single bar indicates one, a double bar indicates one and only one, a circle indicates zero, and a crow's foot indicates many.
data manipulation language (DML)
A data manipulation language controls database operations, including storing, retrieving, updating, and deleting data. Most commercial DBMSs, such as Oracle and IBM's DB2, use a DML.
data mart
A specialized database designed to serve the needs of a specific department, such as sales, marketing, or finance. Each data mart includes only the data that users in that department require to perform their jobs.
data mining
Looking for meaningful patterns and relationships among data. For example, data mining software could help a consumer products firm identify potential customers based on their prior purchases.
data warehouse
An integrated collection of data that can support management analysis and decision making.
database administrator (DBA)
Someone who manages a database management system (DBMS). The DBA assesses overall requirements and maintains the database for the benefit of the entire organization rather than a single department or user.
database management system (DBMS
A collection of tools, features, and interfaces that enables users to add, update, manage, access, and analyze data in a database.
derivation code
Combining data from different item attributes, or characteristics, to build the code. Most magazine subscription codes are derivation codes.
EBCDiC
Stands for Extended Binary Coded Decimal Interchange Code, a coding method used on mainframe computers and some high-capacity servers.
economy of scale
The inherent efficiency of high-volume processing on larger computers. Database design allows better utilization of hardware. If a company maintains an enterprise-wide database, processing is less expensive using a powerful mainframe server instead of using several smaller computers.
entity-relationship diagram (ERD)
A graphical model of the information system that depicts the relationships among system entities.
file
Each file or table contains data about people, places, things, or events that interact with the information system.
file-oriented system
also called a file processing system, stores and manages data in one or more separate files.
first normal form (1NF)
A record is said to be in first normal form (1NF) if it does not contain a repeating group (a set of data items that can occur any number of times in a single record).
foreign key
A field in one table that must match a primary key value in another table in order to establish the relationship between the two tables.
functionally dependent
Functional dependence is an important concept for understanding the second normal form (2NF). The field X is said to be functionally dependent on the field Y if the value of X depends on the value of Y. For example, an order date is dependent on an order number; for a particular order number, there is only one value for the order date. In contrast, the product description is not dependent on the order number. For a particular order number, there might be several product descriptions, one for each item ordered.
international Organization for Standardization (iSO)
A network of national standards institutes from 140 countries working in partnership with international organizations, governments, industry, business, and consumer representatives. The ISO acts as a bridge between public and private sectors.
JDBC (Java database connectivity)
A standard that enables Java applications to exchange data with any database that uses SQL statements and is ODBC-compliant.
key fields
Used during the systems design phase to organize, access, and maintain data structures. The four types of key fields are primary keys, candidate keys, foreign keys, and secondary keys.
logical record
A logical record contains field values that describe a single person, place, thing, or event. Application programs see a logical record as a set of fields, regardless of how or where the data is stored physically.
logical storage
Refers to information as seen through a user's eyes, regardless of how or where that information is organized or stored.
M:N
A type of entity relationship. A many-to-many relationship, abbreviated M:N, exists when one instance of the first entity can be related to many instances of the second entity, and one instance of the second entity can be related to many instances of the first entity.
market basket analysis
A type of analysis that can detect patterns and trends in large amounts of data.
mnemonic code
Ciphers using a specific combination of letters that are easy to remember. Many threecharacter airport codes are mnemonic codes. For example, LAX represents Los Angeles.
multivalued key
Sometimes it is necessary for a primary key to consist of a combination of fields. In that case, the primary key is called a combination key, composite key, concatenated key, or multivalued key.
nonkey field
Any field that is not a primary key or a candidate key is called a nonkey field.
normalization
A process by which analysts identify and correct inherent problems and complexities in their record designs.
ODBC (open database connectivity)
An industry-standard protocol that makes it possible for software from different vendors to interact and exchange data.
orphan
An unassociated or unrelated record or field. An orphan could be created if a customer order was entered in an order table where that customer did not already exist in the customer table. Referential integrity would prevent the creation of this orphan.
permissions
User-specific privileges that determine the type of access a user has to a database, file, or directory. Also called user rights.
physical storage
Information storage mechanism that is strictly hardware-related, because it involves the process of reading and writing binary data to physical media, such as a hard drive, flash drive, or DVD.
primary key
A field or combination of fields that uniquely and minimally identifies a particular member of an entity. For example, in a customer table the customer number is a unique primary key because no two customers can have the same customer number. That key is also minimal because it contains no information beyond what is needed to identify the customer.
query by example (QBE)
A language allows the user to provide an example of the data requested.
query language
Allows a user to specify a task without specifying how the task will be accomplished. Some query languages use natural language commands that resemble ordinary English sentences
recovery procedure
Process for restoring data and restarting a system after an interruption. Recovery procedures can be used to restore a file or database to its current state at the time of the last backup.
referential integrity
A type of validity check. Referential integrity is a set of rules that avoids data inconsistency and quality problems.
relational database
A database in which tables are related by common fields, creating a unified data structure that provides improved data quality and access.
relational model
A model used in relational databases. The relational model was introduced during the 1970s and became popular because it was flexible and powerful.
repeating group
A set of one or more fields that can occur any number of times in a single record, with each occurrence having different values.
schema
The complete definition of a database, including descriptions of all fields, records, and relationships
second normal form (2NF)
A record design is in second normal form (2NF) if it is in 1NF and if all fields that are not part of the primary key are dependent on the entire primary key. If any field in a 1NF record depends on only one of the fields in a combination primary key, then the record is not in 2NF. A 1NF record with a primary key that is a single field is automatically in 2NF.
secondary key
A field or combination of fields that can be used to access or retrieve records. Secondary key values are not unique. For example, to access records for only those customers in a specific postal code, the postal code field could be used as a secondary key.
sequence code
Numbers or letters assigned in a specific order. Sequence codes contain no additional information other than an indication of order of entry into a system.
significant digit code
Cipher that distinguishes items by using a series of subgroups of digits. U.S. Postal Service zip codes, for example, are significant digit codes.
SQL (Structured Query Language)
A query language that allows PC users to communicate with servers and mainframe computers.
standard notation format
A representation that makes designing tables easier as it clearly shows a table's structure, fields, and primary key.
subschema
A view of the database used by one or more systems or users. A subschema defines only those portions of the database that a particular system or user needs or is allowed to access.
table
Each file or table contains data about people, places, things, or events that interact with the information system.
table design
Specifies the fields and identifies the primary key in a particular table or file.
third normal form (3NF)
A record design is in third normal form (3NF) if it is in 2NF and if no nonkey field is dependent on another nonkey field. A nonkey field is a field that is not a candidate key for the primary key.
tuple
A tuple (rhymes with couple), or record, is a set of related fields that describes one instance, or member of an entity, such as one customer, one order, or one product. A tuple might have one or dozens of fields, depending on what information is needed.
Unicode
A relatively recent coding method that represents characters as integers. Unlike EBCDIC and ASCII, which use eight bits for each character, Unicode requires 16 bits per character, which allows it to represent more than 65,000 unique characters.
unnormalized
A record that contains a repeating group, which means that a single record has multiple occurrences of a particular field, with each occurrence having different values.
Y2K issue
A problem faced by many firms in the year 2000 because their computer systems used only two digits to represent the year; most dates now use a four-digit format for the year (YYYYMMDD).
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