Controlled access to database may include?
- a security system
- an integrity system
- a concurrency control system
- a recovery control system
- a user-accessible catalog
Benefits dari Views?
- reduce complexity
- provide a level of security
- provide a mechanism to customize the appearance of the database
- prsent a consistent, unchanging picture of the structure of the database, even if the underlying database is changed
ANSI-SPARC Three-Level Architecture?
- External Level
- Users’ view of the database.
- Describes that part of database that is relevant to a particular user. - Conceptual Level
- Community view of the database.
- Describes what data is stored in database and relationships among the data. - Internal Level
- Physical representation of the database on the computer
- Describes how the data is stored in the database.
2 Jenis dari Data Independence?
- Logical Data Independence
- Refers to immunity of external schemas to changes in conceptual schema.
- Conceptual schema changes (e.g. addition/removal of entities).
- Should not require changes to external schema or rewrites of application programs. - Physical Data Independence
- Refers to immunity of conceptual schema to changes in the internal schema.
- Internal schema changes (e.g. using different file organizations, storage structures/devices)
- Should not require change to conceptual or external schemas
Database Languages?
- Data Definition Language (DDL)
- Data Manipulation Language (DML)
- Procedural DML
Allows user to tell system exactly how to manipulate data. - Non-Procedural DML
Allows user to state what data is needed rather than how it is to be retrieved. - Fourth Generation Languages (4GLs)
What is Data Model?
Data Model is integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization. The purpose of data model is to represent data in an understandable way. Categories of data model: 1. Object-based 2. Record-based 3. Physical
Data Model Comprises of?
- a structural part
- a manipulative part
- possibly a set of integrity rules
What is Conceptual Schema?
Conceptual Schema is the core of a system supporting all user views. Conceptual Schema should be complete and accurate representation of an organization’s data requirements.
What is Conceptual Modeling?
Conceptual modeling is process of developing a model of information use that is independent of implementation details. The result of conceptual modeling is a conceptual data model.
What is System catalog and what system catalog stores?
System catalog is a repository of information (metadata) describing the data in the database. One of the fundamental components of DBMS. Typically stores: 1. names, types and sizes of data times 2. constraints on the data 3. names of authorized users 4. usage statistics 5. user access controls
What is Relationally complete?
relationally complete when a language that produces a relation that can be derived using relational calculus
The differences between relational algebra and relational calculus?
both of them are formal languages associated with the relational model.
Relationaly algebra is a high level procedural language and relational calculus is a non-procedural language.
What is closure?
nested expressions. just as in arithmetic.
Five basic operations in relational algebra?
- selection
- projection
- cartesian product
- union
- set difference
Various forms of join operation?
- Theta join
- Equijoin (a particular type of Theta join)
- natural join
- outer join
- semijoin
5 aggregate functions?
count, sum, max, min, avg
Tuple variable?
tuple variable is a variable that ‘ranges over’ a named relation.
Client-Server advantages?
- wider access to existing databases
- increased performance
- possible reduction in hardware costs
- reduction in communication costs
- increased consistency
6 types of middleware?
middleware is a generic term used to describe software that mediates with other software.
- asynchronous remote procedure call (RPC)
- synchronous RPC
- publish / subscribe
- message-oriented middleware (MOM)
- object-request broker (ORB)
- SQL-oriented data access
What is Transaction processing monitors?
purpose of transaction processing monitors to controls data transfer between clients / servers. provides a consistent environment, particularly for online transaction processing (OLTP). Advantages: 1. trasaction routing 2. managing distributed transactions 3. load balancing 4. funneling 5. increased reliability
the differences between distributed database and distributed DBMS?
distributed database is logically interrelated collection of shared data physically distributed over a computer network.
distributed DBMS is software system that permits the management of the distributed database and makes the distribution transparent to user.
Characteristics of DDBMS?
- data split into fragments
- collection of logically related shared data
- fragments may be replicated
- fragments are allocated to sites
- DBMS handles local apps autonomously
Characteristics of Data Warehouse?
- consolidated / integrated view of corporate data.
- drawn from disparate operational data sources
- range of end-user access tools capable of supporting simple to highly complex queries to support decision making
- subject-oriented, integrated, time-variant and non-volatile.
Components of Database Manager (DM)?
Components of Database manager:
- authorization control
- command processor
- integrity checker
- query optimizer
- transaction manager
- scheduler
- recovery manager
- buffer manager
