Download Computer Science : Databases Midterm COSC 578 and more Exams Computer Science in PDF only on Docsity!
Computer Science : Databases Midterm
COSC 578
data - correct answer Known facts that can be recorded and have implicit meaning database - correct answer collection of related data DBMS (Database Management System) - correct answer A computerized systems that enables users to create and maintain a database. database system - correct answer The database and DBMS software together. Database Catalog - correct answer Definition or description of the database structure and constraints that is stored and contains information such as the structure of each file, the type and storage format of each data item and various constraints on the data. program-data independence - correct answer The structure of data files is stored in the DBMS catalog separately from the access programs. user view - correct answer Users that typically require a different perspective of the database DBA - correct answer Database administrator responsible for authorizing access to the database, coordinating and monitoring its use and acquiring software and hardware resources as needed. end user - correct answer People whose jobs require access to the database for querying, updating and generating reports; the database primarily exists for their use
canned transaction - correct answer Used by naive or parametric end users which constantly query and update the database using standard types that have been carefully programmed and tested. deductive database system - correct answer Provides capabilities for defining deduction rules; inferencing new information from the stored database facts persistent object - correct answer a specialized object that has the property of continuous state, which means it is available at all times meta-data - correct answer data about data. The schema is an example of this. transaction-processing application - correct answer A management information system designed to handle large volumes of routine, recurring transactions. Includes one or more database operations like insertion, deletion, modification and retrieval. What four main types of actions involve databases? - correct answer Database administration, database designing, database users, and system analysis and application programming. Discuss the main characteristics of the database approach and how it differs from traditional file systems. - correct answer 1) Self describing - Complete definitions and descriptions are included (meta-data). Traditionally data definitions are a part of the application programs themselves. 2) Insulation between programs and data and data abstraction - The structure of data files stored separately. Traditionally, structure of data files is embedded in application programs so any changes to the structure requires changing all programs. 3) Support of multiple views of data - Traditionally, multiple views not supported. 4) Sharing of data and multi-user transaction process - DBMS allows multiple users to access database at same time. Traditionally, data sharing is possible. Discuss the capabilities that should be provided by a DBMS. (8) - correct answer 1) Controlling redundancy
- Restricting unauthorized access
Database designing - correct answer Identifying the data to be stored in the database and to choose appropriate data structures to represent and store the data. Should fulfill the requirements of all user groups of the organization. Database user - correct answer Causal, parametric, sophisticated, and standalone end users. Casual end user - correct answer occasionally accessing the database like middle and high-level managers Parametric end user/naive - correct answer Constantly querying and updating the database, such as bank tellers and reservation clerks Sophisticated end users - correct answer Engineers, scientists, etc who are experts at using the DB, and develop applications on top of a databases. Standalone users - correct answer maintain personal databases by using ready-made program packages that provide easy-to-use menu-based or graphics-based interfaces System analysis and application programming - correct answer Includes the determination of requirements for end users and develops specifications for canned transactions, includes testing developing, documentation and maintaining recorded transactions, associated with software development or software engineering data model - correct answer describes the logical structure of the database and it introduces abstraction. Provides a tool to describe the data and their relationships. database schema - correct answer describes the overall design of the database. A basic structure to define how the data is organized in the database. The database schema can be depicted by the schema diagrams. database state - correct answer actual data stored in the database in a moment in time
internal schema - correct answer physical level schema. Represents the structure of the data as viewed by the DBMS and it describes the physical storage structure of the database. conceptual schema - correct answer Logical level schema. Describes the logical structure of the whole database for a group of users. Hides the internal details of the physical storage structure. External schema - correct answer User level schema. Describes the data which is viewed by the end users. Describes the part of the database for a user group and hides the rest of the database from that user group. Data independence - correct answer Capacity to change the schema at the physical level of a database system without affecting the schema at the conceptual or external level. DDL (Data Definition Language) - correct answer used to create, alter, and drop the database tables, views, and indexes. DML (Data Manipulation Language) - correct answer Used to insert, retrieve, update, and delete the records in the database SDL (storage definition language) - correct answer Used to specify the internal schema of the database and specify the mapping between two schemas. VDL (View Definition Language) - correct answer Specifies the user views and their mappings to the logical schema in the database Query language - correct answer High-level language used to retrieve data from the database Host language - correct answer Used for application programming in a database. The DML commands are embedded in a general-purpose language to manipulate the data in the database.
to conceptual data models. Classes in the object model are designed in acyclic graphs. (Doc O Model) What are the basic differences among the XML model? - correct answer Hierarchical. Data can be defined in a single XML document. The data doesn't have ordering. It's represented in tags known as elements. (Stylus Studio) Difference between the database schema and the database state - correct answer The database schema is an intension - specified during database design and is not expected to change frequently. Displays the structure of each record type but not the actual instances of records. Database state - Current set of occurrences. Describe the three-schema architecture. Why do we need mappings among schema levels? How do different schema definition languages support this architecture? - correct answer Separate the user applications and physical database. Has an internal schema which describes the physical storage structure and conceptual schema which describes the structure of the whole database for a community of users. Also has an external level which describes part of the database that a particular user group is interested in and hides the rest of the database. We need mappings to transform requests and results between levels as well as defines correspondence between conceptual view and stored database. Also an external conceptual mapping defines he correspondence between an external view and the conceptual view. Discuss the role of a high-level data model in the database design process. - correct answer 1) Does not include implementation details - to make it easier to understand and communicate to non-technical users
- It is a reference that can be used to ensure that requirements are met.
- Enables designers to concentrate on specifying the properties of data without being concerned with storage details. List the various cases where use of a NULL value would be appropriate. - correct answer 1) When value of an attribute is irrelevant.
- When the value is not known
Entity - correct answer Object with independent physical (car, home, person) or conceptual (company, university course) existence in the real world Attribute - correct answer Each real world entity (thing) has certain properties that represent its significance in the real world or describes it. Attribute value - correct answer Attributes that are associated with an entity and describe it. Relationship instance - correct answer Association of entities where the association includes exactly one entity from each participating entity type. Each such relationship instances represent the fact that the entities participating in are related in some way in the corresponding miniworld situation. They link 2 or more different entities together. Composite attribute - correct answer can be divided into smaller components, which represent more basic attributes that have their own meanings multivalued attribute - correct answer having the potential to contain more than one value for an attribute derived attribute - correct answer values can be calculated from related attribute values. Complex attribute - correct answer Composite and multivalued that can be nested arbitrarily. For example a person having multiple addresses and phone numbers. key attribute - correct answer Value is different for all similar types of entities. Entity type - correct answer A collection or set of entities that have the same attributes. Same attributes but different attribute values Entity set - correct answer Collection of entitites of an entity type at an instance of time
identifying relationship type - correct answer relates a weak entity to its owner entity type Partial key - correct answer set of attributes in weak entity types that can uniquely identify weak entities that are related to the same owner entity Subclass - correct answer the subordinate or more specialized class in a generalization/specialization relationship. The same as the entity in the superclass but in a distinct role. What are the four operations of relational algebra? - correct answer Union, intersection, difference, cartesian product What are the specific operations for relational databases - correct answer Unary: (Select, project, rename), Binary: (Join, division), Additional: (outer joins, outer union, aggregate functions) union - correct answer relation that includes all the tuples that are either in R or in S or both. Duplicate tuples are eliminated. intersection - correct answer Includes all tuples that are in both R and S difference - correct answer Of R and S is the relation that contains all tuples that are in R but not in S Cartesian Product - correct answer Combines the tuples of one relation with all the tuples of the other relation Select - correct answer Obtain a subset of the tuples of a relation that satisfy a condition
Project - correct answer Select a subset of the attributes of a relation Join - correct answer Combine related tuples from two relations Union compatibility - correct answer Both relations have the same number of attributes and the domain of the similar attributes is the same 4 clauses in the syntax of a simple SQL retrieval query - correct answer Select, from, where, order by
