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Terms in this set (107)Ad hoc query spur-of-the-moment question update anomaly not updating all redundant phone number fields for a customer who's phone number changes insertion anomaly if you only have a CUSTOMER table, but add a new agent, a dummy customer needs to be created to display the agent data deletion anomaly you delete customer records, deleting an agent's data data dependence all data access programs are subject to change when any of the file's data storage characteristics change data independence you can change the data storage characteristics without affecting the program's ability to access the data desktop database A single-user database that runs on a personal computer field A character or group of characters (alphabetic or numeric) that has a specific meaning. A field is used to define and store data. file A collection of related records nosql generally used to describe a new generation of database management systems that is not based on the traditional relational database model record A logically connected set of one or more fields that describes a person, place, or thing. For example, the fields that constitute a customer record might consist of the customer's name, address, phone number, date of birth, credit limit, and unpaid balance. structural dependence access to a file is dependent on its structure structural independence exists when you can change the file structure without affecting the application's ability to access the data. attribute a characteristic of an entity. For example, a CUSTOMER entity would be described by attributes such as customer last name, customer first name. business rule a brief, precise, and unambiguous description of a policy, procedure, or principle within a specific organization conceptual model represents a global view of the entire database by the entire organization. That is, the conceptual model integrates all external views (entities, relationships, constraints, and processes) into a single global view of the data in the enterprise) conceptual schema it is the basis for the identification and high-level description of the main data objects constraint a restriction placed on the data. Constraints are important because they help to ensure data integrity. Constraints are normally expressed in the form of rules. ( gpa must be between 0 and 4) Data model a relatively simple representation, usually graphical, of more complex real-world data structures entity instance Each row in the relational table eventual consistency updates to the database will propagate through the system and eventually all data copies will be consistent. With eventual consistency, data are not guaranteed to be consistent across all copies of the data immediately after an update. Extensible Markup Language (XML) de facto standard for the efficient and effective exchange of structured, semistructured, and unstructured data External model the end users' view of the data environment. external schema A specific representation of an external view (register for classes) Hardware independence the model does not depend on the hardware used in the implementation of the model. Therefore, changes in either the hardware or the DBMS software will have no effect on the database design at the con- ceptual level internal model the representation of the database as "seen" by the DBMS. In other words, the internal model requires the designer to match the conceptual model's characteristics and constraints to those of the selected implementation model. Key-value The key-value data model is based on a structure composed of two data elements: a key and a value, in which every key has a corresponding value or set of values. Logical design refers to the task of creating a conceptual data model that could be implemented in any DBMS logical independence When you can change the internal model without affecting the conceptual model physical model operates at the lowest level of abstraction, describing the way data are saved on storage media such as disks or tapes physical independence When you can change the physical model without affecting the internal model relation you can think of a relation (sometimes called a table) as a matrix composed of intersecting rows and columns tuple Each row in a relation relational database management system (RDBMS) the relational data model is implemented through a very sophisticated relational database management system (RDBMS). The RDBMS performs the same basic functions provided by the hierarchical and network DBMS systems, in addition to a host of other functions that make the relational data model easier to understand and implement. relational diagram a representation of the relational database's entities, the attributes within those entities, and the relationships between those entities Relational model The relational model represented a major breakthrough for both users and designers. To use an analogy, the relational model produced an "automatic transmission" database to replace the "standard transmission" databases that preceded it. relationship describes an association among entities. For example, a relationship exists between customers and agents that can be described as follows: an agent can serve many customers schema the conceptual organization of the entire database as viewed by the database administrator sparse data NoSQL databases can handle very high volumes of data. In particular, they are suited for sparse data—that is, for cases in which the number of attributes is very large but the number of actual data instances is low. domain the column's range of permissible values key consists of one or more attributes that determine other attributes Determination The state in which knowing the value of one attribute makes it possible to determine the value of another. The role of a key is based on the concept of determination. functional dependence the value of one or more attributes determines the value of one or more other attributes determinant any attribute whose value determines other values within a row. If you have three different transitive dependencies, you will have three different determinants dependent The attribute whose value is determined by the other attribute full functional dependence functional dependencies in which the entire collection of attributes in the determinant is necessary for the relationship. For example, "{SSN, age} -> name" is a functional dependency, but it is not a full functional dependency because you can remove age from the left side of the statement without impacting the dependency relationship. Key attribute / prime attribute An attribute that is a part of a key superkey a key that can uniquely identify any row in the table candidate key a minimal superkey—that is, a superkey without any unnecessary attributes. A candidate key is based on a full functional dependency. Entity integrity the condition in which each row (entity instance) in the table has its own unique identity. To ensure entity integrity, the primary key has two requirements: (1) all of the values in the primary key must be unique, and (2) no key attribute in the primary key can contain a null. Referential integrity the condition in which every reference to an entity instance by another entity instance is valid. In other words, every foreign key entry must either be null or a valid value in the primary key of the related table. secondary key a key that is used strictly for data retrieval purposes. Suppose that customer data are stored in a CUSTOMER table in which the customer number is the primary key. Do you think that most cus- tomers will remember their numbers? Data retrieval for a customer is easier when the customer's last name and phone number are used. union-compatible When two or more tables share the same number of columns, and when their corresponding columns share the same or compatible domains natural join links tables by selecting only the rows with common values in their common attribute(s) inner join inner join only returns matched records from the tables that are being joined. natural join falls in this. outer join the matched pairs would be retained, and any unmatched values in the other table would be left null. left outer join yields all of the rows in the first (left) table, including those that do not have a matching value in the second (right) table (leaves them null). Right outer is opposite synonym indicates the use of different names to describe the same attribute. For example, car and auto refer to the same object. Synonyms must be avoided homonym the use of the same name to label different attributes. For example, you might use C_NAME to label a customer name attribute in a CUSTOMER table and use C_NAME to label a consultant name attribute in a CONSULTANT table. To lessen confusion, you should avoid database homonyms; bridge entity/associative entity/linking table a table is used to link the tables that were originally related in an M:N relationship, the composite entity structure includes—as foreign keys—at least the primary keys of the tables that are to be linked. index an orderly arrangement used to logically access rows in a table unique index index key can have only one pointer value (row) associated with it data dictionary provides a detailed description of all tables in the database created by the user and designer binary relationship exists when two entities are associated. Professor teaches class. ternary relationship exists when three entities are associated. Doctor prescribes patient a drug. unary relationship/recursive relationship exists when an association is maintained within a single entity. Employee manages employee. Composite attribute an attribute that can be further subdivided to yield additional attributes. For example, the attribute ADDRESS can be subdivided into street, city, state, and zip code. Similarly, the attribute PHONE_NUMBER can be subdivided into area code and exchange number. Simple attribute an attribute that cannot be subdivided. For example, age, sex, and marital status would be classified as simple attributes. multivalued attribute attributes that can have many values. For instance, a person may have several college degrees, and a household may have several different phones Single-valued attribute Only one value. SSN, serial number participants The entities that participate in a relationship Connectivity used to describe the relationship classification in cardinality Existence-dependent it can exist in the database only when it is associated with another related entity occurrence. In implementation terms, an entity is existence-dependent if it has a mandatory foreign key—that is, a foreign key attribute that cannot be null. For example, if an employee wants to claim one or more dependents for tax-withholding purposes, the relationship "EMPLOYEE claims DEPENDENT" would be appropriate. In that case, the DEPENDENT entity is clearly existence-dependent on the EMPLOYEE entity because it is impossible for the dependent to exist apart from the EMPLOYEE in the database. Existence-independent/strong entity/regular entity an entity can exist apart from all of its related entities. For example, suppose that the XYZ Corporation uses parts to produce its prod- ucts. Furthermore, suppose that some of those parts are produced in-house and other parts are bought from vendors. In that scenario, it is quite possible for a PART to exist independently from a VENDOR in the relationship "PART is supplied by VENDOR," because at least some of the parts are not supplied by a vendor. Therefore, PART is existence- independent from VENDOR. weak relationship/non-identifying relationship exists if the primary key of the related entity does not contain a primary key component of the parent entity. If the parent entity PK is the FK in the related entity. strong relationship/identifying relationship exists when the primary key of the related entity contains a primary key component of the parent entity weak entity 1. The entity is existence-dependent; it cannot exist without the entity with which it has a relationship. Optional participation one entity occurrence does not require a corresponding entity occurrence in a particular relationship. For example, in the "COURSE generates CLASS" relationship, you noted that at least some courses do not generate a class. Mandatory participation one entity occurrence requires a corresponding entity occurrence in a particular relationship. If no optionality symbol is depicted with the entity, the entity is assumed to exist in a mandatory relationship with the related entity. derived attribute an attribute whose value is calculated (derived) from other attributes. The derived attribute need not be physically stored within the database; instead, it can be derived by using an algorithm. For example, an employee's age, EMP_AGE, may be found by computing the integer value of the difference between the current date and the EMP_DOB. optional attribute an attribute that does not require a value; therefore, it can be left empty. required attribute n attribute that must have a value; in other words, it cannot be left empty. Boldfaced attributes in the Crow's Foot notation indicate that data entry will be required. identifier one or more attributes that uniquely identify each entity instance. In the relational model, entities are mapped to tables, and the entity identifier is mapped as the table's primary key (PK). Completeness constraint Specifies whether each entity supertype occurrence must also be a member of at least one subtype. The completeness constraint can be partial or total. Partial completeness not every super- type occurrence is a member of a subtype; some supertype occurrences may not be members of any subtype. (one line on connector) total completeness means that every supertype occurrence must be a member of at least one subtype. (two lines on connector) entity supertype/subtype entity supertype is a generic entity type that is related to one or more entity subtypes. The entity supertype contains common characteristics, and the entity subtypes each contain their own unique characteristics. Employee --> Mechanic Two criteria that help the designer determine when to use subtypes and supertypes: 1) There must be different, identifiable kinds or types of the entity in the user's environment. Specialization hierarchy Organizes entity supertypes and subtypes. Depicts the arrangement of higher-level entity supertypes (parent entities) and lower-level entity subtypes (child entities). Specialization hierarchy formed by an EMPLOYEE supertype and three entity subtypes—PILOT, MECHANIC, and ACCOUNTANT. inheritance enables an entity subtype to inherit the attributes and relationships of the supertype. As discussed earlier, a supertype contains attributes that are common to all of its subtypes.
subtype discriminator the attribute in the supertype entity that determines to which subtype the supertype disjoint subtype each entity instance of the supertype can appear in only one of the subtypes. overlapping subtype each entity instance of the supertype may appear in more than one subtype. Specialization the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype. Specialization is based on grouping the unique characteristics and relationships of the subtypes. In the aviation example, you used specialization to identify multiple entity subtypes from the original employee super- type Generalization the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes. Generalization is based on grouping the common characteristics and relationships of the subtypes. For example, you might identify multiple types of musical instruments: piano, violin, and guitar. Using the generalization approach, you could identify a "string instrument" entity supertype to hold the common characteristics of the multiple subtypes natural key/natural identifier a real-world, generally accepted identifier used to distinguish—that is, uniquely identify—real-world objects. As its name implies, a natural key is familiar to end users and forms part of their day-to-day business vocabulary. surrogate key primary key created by the database designer to simplify the identification of entity instances. The surrogate key has no meaning in the user's environment—it exists only to distinguish one entity instance from another. One practical advantage of a surrogate key is that because it has no intrinsic meaning, values for it can be generated by the DBMS to ensure that unique values are always provided. denormalization produces a lower normal form; that is, a 3NF will be converted to a 2NF through denormalization. However, the price you pay for increased performance through denormalization is greater data redundancy. normalization a process for evaluating and correcting table structures to minimize data redundancies, thereby reducing the likelihood of data anomalies. partial dependency exists when there is a functional dependence in which the determinant is only part of the primary key repeating group derives its name from the fact that a group of multiple entries of the same type can exist for any single key attribute occurrence. repeating groups means the table isn't even in 1 NF. For example, a book might have multiple authors. 1NF 1) All of the key attributes are defined. 2NF 1) It is in 1NF. 3NF 1) It is in 2NF.
granularity refers to the level of detail represented by the values stored in a table's row. Data stored at their lowest level of granularity are said to be atomic data, as explained earlier. ASSIGN_HOURS --> WEEKLY_ASSIGN_HOURS atomic attribute one that can- not be further subdivided. Such an attribute is said to display atomicity. (EMP NAME --> EMP L Name) Boyce-Codd Normal Form Boyce-Codd normal form (BCNF) when every determinant in the table is a candidate key. (Recall from Chapter 3 that a candidate key has the same characteristics as a primary key, but for some reason, it was not chosen to be the primary key.) Clearly, when a table contains only one candidate key, the 3NF and the BCNF are equivalent. Recommended textbook solutions
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COMPUTER SCIENCE One logic function that is used for a variety of purposes (including within adders and to compute parity) is exclusive OR. The output of a two-input exclusive OR function is true only if exactly one of the inputs is true. Show the truth table for a two-input exclusive OR function and implement this function using AND gates, OR gates, and inverters. Verified answer COMPUTER SCIENCE A hand consists of 1 card drawn from a standard 52-card deck with flowers on the back and 1 card drawn from a standard 52-card deck with birds on the back. A standard deck has 13 cards from each of 4 suits (clubs, diamonds, hearts, spades). The 13 cards have face value 2 through 10, jack, queen, king, or ace. Each face value is a “kind” of card. The jack, queen, and king are “face cards.” How many hands contain at least 1 face card? Verified answer Other Quizlet setstest 128 terms meshalove93 CH 38- Transport Operations56 terms tiff_nguyen23 Community Health Final Exam30 terms melissa86082PLUS Exam 2 OChemL20 terms edwardsj04 Related questionsQUESTION Matrix Diagrams are developed BEFORE the ERD. True or False? 14 answers QUESTION 48) One way to generate messages for near-real-time replication is through the use of database triggers. 4 answers QUESTION
What data type would be the most logical to use for a field named InvoicePaid if an invoice has not been paid? 2 answers QUESTION The minus symbol at the left of a record in a related table with a sub datasheet displayed is referred to as this. 2 answers What are the two conditions for using Supertype subtype relationships?Two conditions that indicate a designer should consider using supertype/subtype relationships: There are attributes that apply to some (but not all) of the instances of an entity type. The instances of a subtype participate in the relationship unique to that subtype.
What is an entity supertype and subtype and why is it used?A supertype is a generic entity type that has a relationship with one or more subtypes. A subtype is a sub-grouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroups.
When should subtypes be used?Subtypes should be used when: there are attributes that apply to some but not all instances of an entity type. The process of defining one or more subtypes of a supertype and forming relationships is called: specialization.
Which of the following is the primary reason for using entity Supertypes?The reason for using supertypes is to minimize nulls and redundant relationships. contain more specific ,the unique characteristics of each entity subtype.
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Which of the following two criteria help the designer determine when to use subtypes and supertypes?
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