Database Terms And Internet Terms Flashcards
Data
- smallest unit of info
- eg employees hourly wage rate
- processed and stored as bits and bytes
- data is raw numbers and information is processed data
Record
- a log for eg of employees hourly wage rate, hours worked in a week
File
A collection of related records. An example is a payroll file containing payroll records.
Directory
The list of files stored on a disk (e.g., payroll directory).
Dataset
A collection of related bytes, or characters, of secondary storage. For example, a dataset may be a file of payroll records or a library of payroll programs.
In z/OS, a data set is a named collection of related data records that is stored and retrieved by an assigned name. A data set is equivalent to a file in other operating systems. Data sets are stored on tape or disks.
Database
A collection of interrelated data stored together, using a common and controlled approach (e.g., payroll)
Database System
Data is maintained independently of the application programs.
Data can be shared by many programs and users.
Database management system (DBMS) software manages and controls the data and the database software.
Data Dictionary
Contains attributes and characteristics of each data element or field in a computer record. It also includes file organization and structure and edit and validation rules.
Schema
A set of specifications that defines a database.
Specifically, it includes entity names, sets, groups, data items, areas, sort sequences, access keys, and security locks.
A logical view of an entire database is called a schema. Schemas may be external, conceptual, or internal. A synonym for the word “schema” is “view.”
Subschema
A subset of a schema. It represents a portion of a database as it appears to a user or application program.
A subschema is a part of schema. In other words, a schema is made up of one or more subschemas.
Subject
A person who is using a computer system (e.g., employee, contractor, and consultant).
Object
A passive entity that contains or receives information. Examples of objects are data, records, blocks, files, and programs.
Access
A specific type of interaction between a subject (e.g., user) and an object (e.g., data) that results in the flow of information from one to the other.
Check-point
A point, generally taken at regular intervals, at which a program’s intermediate results are dumped to a secondary storage (e.g., disk) to minimize the risk of work loss. Databases operate on checkpoints.
Deadlock
A consequence of poor resource management
Occurs when two programs each control a resource (e.g., printer, data file, database, and record) needed by the other and neither is willing to give in its resource.
Databases can run into deadlocks.
Tuple
A row of a relational table in a relational database.
Rollback
Restores the database from one point in time to an earlier point.
Roll forward
Restores the database from a point in time when it is known to be correct to a later time.
Recovery
The process of reconstituting a database to its correct and current state following a partial or complete hardware, software, network, operational, or processing error or failure.
What is a DBMS comprised of?
Software, hardware and procedures
What should the DBMS be compatible with?
The OS
Advantages of a DBMS
1) Min. Data redundancy resulting in data consistency
2) Data independence from application programs except during computer processing
3) Consistent and quality information for decision making
4) Adequate security and integrity controls
5) Shared access to data
6) Single storage location for each data item
7) Built in backup and recovery procedures
Disadvantages of a DBMS
1) Can be expensive to acquire, operate, and maintain.
2) Requires additional main memory.
3) Requires additional disk storage.
4) Requires knowledgeable and technically skilled staff (e.g., database administrator [DBA] and data administrator).
5) Results in additional system overhead, thereby slowing down the system response time.
6) Needs additional CPU processing time.
7) Requires sophisticated and efficient security mechanisms.
8) Is difficult to enforce security protection policies.
When is redundancy of data sometimes necessary?
When high system performance and high data availability are required.
What is the trade-off with regards to the redundancy of data?
The trade-off here is the cost of collecting and maintaining the redundant data and the system overhead it requires to process the data. Another concern is synchronization of data updates in terms of timing and sequence. Ideally, the synchronization should be done at the system level rather than the application level.
What is the primary function of a DBMS?
Store data and to provide operations on the database.
Operations usually include create, delete, update, and search of data.
What are the essential features supported by most DBMS?
1) Persistence - is the property wherein the state of the database survives the execution. Of a process in order to be reused later in another process.
2) Data sharing - is the property that permits simultaneous use of the database by multiple users.
3) Recovery - Refers to the capability of the DBMS to return its data to a consistent and coherent state after a hardware or software failure.
4) Database language - permits external access to the DBMS.
5) Security and integrity - security and authorisation control, integrity checking, utility programs, backup/archiving, versioning, and view definition.
A DBMS that permits sharing must provide what control?
Concurrency control (locking) mechanism that prevents users from executing inconsistent actions on the database.
Name database languages
Data definition language (DDL) - used to define database schema and subschema
Data manipulation language (DML) - used to examine and manipulate contents of the database
Data control language (DCL) - used to specify parameters needed to define the internal organisation of the database such as indexes and buffer size.
Ad hoc query language - is provided for interactive specification of queries.
Name 2 types of integrity checking
Semantic - declaration of semantic and structural integrity rules and the enforcement of these rules. May be automatically enforced at program run time or at compile time or may be performed only when a message is sent.
Referential - No record may contain a reference to the primary key of a non existent record
Describe the relationship among database models
User needs - Conceptual model or user views - logical/external model - physical/internal model
- User requirements are specified to conceptual model first (user views).
- When the conceptual model is presented to the DBMS, it becomes a logical model/external model/schema/subschema.
- The logical model is converted to a physical model(internal model) in terms of physical storage media such as magnetic disks, tapes, disk arrays.
Describe dependencies between DBMS and conceptual model.
The type of DBMS is not a factor in designing a conceptual model, but the design of a logical model is dependent on the type of DBMS to be used.
This means that the conceptual model is, or should be, independent of a DBMS.
Logical Database Design
- process of determining an information system structure that is independent of software or hardware considerations.
- It produces logical data structures consisting of a number of entities connected by one-to-one or one-to-many relationships, subject to appropriate integrity checking.
- The objective is to improve the effectiveness of an information system by maximizing the accuracy, consistency, integrity, security, and completeness of the database.