Basic Concepts Flashcards
define database
A collection of related data.
data
known facts that can be recorded and have an implicit meaning.
mini-world
Some part of the real world about which data is stored in a database. For example, student grades and transcripts at a university.
data-base management system (DBMS)
A collection of programs to facilitate the creation and maintenance of a computerized database
database system
The DBMS software together with the data itself. Sometimes, the applications are also included
A DBMS is a general purpose software system that facilitates the process of ____, ____, and ____ DBs for various applications.
defining, constructing, and manipulating
_____ a DB involves specifying the data types, structures and constraints for the data to be stores in the DB.
Defining
____ a DB is the process of storing the data itself on some storage medium that is controlled by the DBMS.
Constructing
Manipulating a DB involves functions such as ____ the DB to retrieve specific data, ___ the DB to reflect changes in the mini-world, and _____ from the data.
querying; updating; generating reports
describe the self-contained nature of database system.
Self-contained nature of database system: A DBMS catalog stores the description of the database. (The description is called meta-data) This allows the DBMS software to work with different databases.
The characteristic that allows program-data independence is called _______.
data abstraction Insulation between programs and data: Called program-data independence. Allows changing data storage structures and operations without having to change the DBMS access programs.
data model
A set of concepts to describe the structure of a database. A data model is a type of data abstraction that is used to provide the users with a conceptual representation of data that does not include many of the details of how data is stored.
Why is multiple views a good characteristic of the database approach?
Support of multiple views of the data: Each user may see a different view of the database, which describes only the data of interest to that user.
concurrency control w.r.t. DBMS
The DBMS must include concurrency control software to ensure that multiple users trying to update the same data do so in a controlled manner so that the result of the update is correct.
List four groups of people who might interact with a database
database administrators database designers end users system analysts and application programmers
When not to use a DBMS
- If the database and applications are simple, well defined, and not expected to change.
- If there are stringent real time requirements that may not be met because of DBMS overhead.
- If access to data by multiple users is not required. Sometimes no DBMS may suffice:
- If the database system is not able to handle the complexity of data because of modeling limitations.
The ____ of a database refers to the data types, relationships, and constraints that the database should obey.
structure
A data model can also contain _______ that specify database retrievals and updates by referring to the concepts of the data model.
user-defined operations
Name 3 Categories of data models
conceptual, physical, and implementation
conceptual data models
high-level, semantic data models; provide concepts that are close to the way many users perceive data. Also called entity-based or object-based data models.
physical data models
low-level, internal data models; provide concepts that describe details how how data is stored in the computer.
implementation
record-oriented data models; Provide concepts that fall between conceptual and physical data models, balancing user views with some computer storage details.
database schema
The description of a database. Includes descriptions of the database structure and the constraints that should hold on the database.
schema diagram
A diagrammatic display of some aspect of a database system.
database instance
The actual data stored in a database at a particular moment in time. Also called database state (or occurence).
The database schema changes very ______. The database state changes __________.
infrequently; every time the database is updated
Schema is also called
intension
State, or instance, is sometimes called
extension
What are the three levels of the three level architecture?
internal schema, conceptual schema, external schema
What characteristics of the database approach is the three level architecture proposed to support?
program-data independence and multiple views of the data.
Internal schema
the internal level to describe data storage structures and access paths. Typically uses a physical data model.
Conceptual schema
at the conceptual level to descrive the structure and constrains for the whole database. Uses a conceptual or an implementation data model.
External schemas
at the external level to descrive the various user views. Usually uses the same data model as the conceptual level.
_____ among schema levels are also needed.
Mappings. Programs refer to an external schema, and are mapped by the DBMS to the interal schema for execution.
logical data independence vs. physical data indepence
logical data independence is the capacity to change the conceptual schema without having to change the external schemas and their application programs.
physical data independence is the capacity to change the inernal schema without having to change the coneptual schema.
When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS that fully supports data independece. The higher level schemas themselves are _____.
unchanged; Hence, the application programs need not be changed since they refer to the external shemas
data definition language
Used by the DBA and database designers to specify the conceptual schema of a database.
In many DBMSs, the DDL is also used to define _____ and _____ schemas(views)
internal and external
In some DBMSs, separate ________ and _________ are used to define internal and external schemas respectively.
storage definition language (SDL) and view definition language (VDL)
data manipulation language (DML)
Used to specify database retrievals and updates.
In current DBMS a _________ is used that includes constructs for conceptual schema definiton, view definition, and schema, and data manipulation.
comprehensive integrated language
DML commands (data sublanguage) can be embedded in a general-purpose programmign language (host language), such as COBOL, PL/1 or PASCAL.
Alternatively, stand alone DML commands can be applied directly (query language).
A DML that can be used on its own to specify complex DB operations in a conside manner is called ___________.
high-level DML (as oppose to a low-level DML)
A ________ DML can specify and retrieve many records in a single DML statement (_______ DML). A low-level DML retrieves and process each time one record from a set of records (_______ DML)
high-level; set-at-a-time; record-at-a-time
A query in a high-level DML often specifies which data to retrieve (________) rather than how to retrieve it (________)
declarative; procedural language
The ____________ is used to store schema decriptions and other information such as design decisions, application program descriptions, user information, usage standards, etc.
data dictionary / repository
object data mdoel
The Object data model defines a database in terms of objects, their properties, and their operations. Objects belong to classes; classes are organzied into hierarchies; the operations of each class are specified in terms of predefined procedures called methods.
network data model
The Network data model represents data as record types and 1:N relationships (called set types).
It has an associated record-at-a-time language that must be embedded in a host programming language.
hierarchical data model
The Hierarchical data model represents data as hierarchical tree structures (parent-child relationship types)
There is no standard language. Most hierarchical DBMS use a record-at-a-time language.
