dbms additional review

Domain Constraints.

A domain of possible values must be associated with every attribute (for example, integer types, character types, date/time types).

Referential Integrity.

There are cases where we wish to ensure that a value that appears in one relation for a given set of attributes also appears in a certain set of attributes in another relation (referential integrity). For example, the department listed for each course must be one that actually exists.

Assertions

. An assertion is any condition that the database must always satisfy. Domain constraints and referential-integrity constraints are special forms of assertions.

Authorization

• . We may want to differentiate among the users as far as the type of access they are permitted on various data values in the database

Sophisticated users

interact with the system without writing programs. Instead, they form their requests in a database query language. They submit each such query to a query processor, whose function is to break down DML statements into instructions that the storage manager understands. Analysts who submit queries to explore data in the database fall in this category.

application development (RAD)

tools are tools that enable an application programmer to construct forms and reports without writing a program.

Online analytical processing (OLAP)

tools simplify analysts’ tasks by letting them view summaries of data in different ways.

 

data mining

Another class of tools for analysts is ____ tools, which help them find certain kinds of patterns in data.

Specialized users

are sophisticated users who write specialized database applications that do not fit into the traditional data-processing framework.

Authorization and integrity manager

, which tests for the satisfaction of integrity constraints and checks the authority of users to access data.

Transaction manager

, which ensures that the database remains in a consistent (correct) state despite system failures, and that concurrent transaction executions proceed without conflicting.

File manager

, which manages the allocation of space on disk storage and the data structures used to represent information stored on disk.

Buffer manager,

which is responsible for fetching data from disk storage into main memory, and deciding what data to cache in main memory. The buffer manager is a critical part of the database system, since it enables the database to handle data sizes that are much larger than the size of main memory.

Domain of Attributes

The set of possible values that an attribute can take is called the domain of the attribute.

Key attribute

The attribute (or combination of attributes) which is nique for every entity instance

Derived Attribute

An attribute which can be calculated or derived based on other attributes is a derived attribute.

Example for derived attribute : age of employee which can be calculated from date of birth and current date.  

Relationships

Associations between entities

domain

For each attribute of a relation, there is a set of permitted values, called the ___ of that attribute

atomic

A domain is ___ if elements of the domain are considered to be indivisible units.

null

The ____ value is a special value that signifies that the value is unknown or does not exist.

candidate keys.

. Such minimal superkeysare called

primary key

We shall use the term ____ to denote a candidate key that is chosen by the database designer as the principal means of identifying tuples within a relation.

•Primary key attributes are also underlined. A relation, say r1, may include among its attributes the primary key of another relation, say r2. This attribute is called a foreign key from r1, referencing r2.

•The relation r1 is also called the referencing relation of the foreign key dependency, and r2 is called the referenced relation of the foreign key.

•The constraint from section to teaches is an example of a referential integrity constraint; a referential integrity constraint requires that the values appearing in specified attributes of any tuple in the referencing relation also appear in specified attributes of at least one tuple in the referenced relation.