12.Data Dictionary

8/4/2019 12.Data Dictionary

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Data Dictionary Nature of a Data Dictionary (DD) Rationale for a DD

Structure of a DD Typical DD Contents

Using SQL to View DD in Oracle

grant and revoke Statements


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Nature of a DD A database contains information about entities

of interest to users in an organization When created, the database itself becomes

an entity about which information must bekept for various data administration purposes

Data dictionary(or system catalog)is adatabase about the database

Contents of a DD are commonly referred to as

metadata DD can be updated, queried much as aregular database

DBMS often maintains the DD


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Rationale for a DD Provides a summary of the structure of thedatabase helps DBA manage the database

informs users of database scope Facilitates communication between users and

database administrators

Allows the DBMS to manage the creation,

access, and modification of tables and theircomponents


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Structure of a DD DD can be integratedwith the DBMS or

stand-alone

Relational systems all have some form ofintegrated DD (e.g., Oracle)

Integrated DD is usually active, meaning it isautomatically updated to reflect changes in

the database A stand-alone DD is not directly linked to the

database and must be updated manually


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Typical DD Contents Data elements

names, data type

Tables owner, creation date, access specifications, size

Indexes name, attributes involved, creation date

Authorized users names, type(s) of access

Integrity Constraints


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Some Oracle DD (Catalog) Tables SYS.OBJ$

contains, for each database object, such data asobject name, owner (number), creation time

Can view details with describe sys.obj$

Sample query

select name, ctimefrom sys.obj$

where ctime > 01-feb-02;


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SYS.COL$ Contains, for each column, such data as data type,

table, whether nulls are allowed, and position in

table

View with describe sys.col$

Sample query select obj#

from sys.col$

where upper(name) = city;


Some Oracle DD (Catalog) Tables


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SYS.IND$

Contains the indexes defined for every table

describe sys.ind$

select i.ind#, o.name

from sys.ind$ i, sys.obj$ o

where i.obj# = o.obj#;

select count(*) from sys.ind$;

SYS.USER$

Contains name, password, and other informationabout each user

select password from sys.user$

where name = jparsons;




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SYS.VIEW$

Contains information about defined views

describe sys.view$

select * from sys.view$;

SYS.TAB$

Contains administrative information about tables

There are many additional system tables inthe Oracle data dictionary




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COMMENT ON statement

Can put comments on each database object as ageneral description of that object

comment ontable orders

is Contains all unfilled orders;

comment on

column orders.dollars

is Total value = qty*products.price;

Using Comments to DescribeDatabase Objects


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select comment$ from sys.com$

where col# is null

and obj# in

(select obj# from sys.obj$where name = orders);

The DD contains a lot of information we may notwant to be generally available

Possible to create views such that users can seedata related only to tables created by themselves

Tables owned by sys (the DBA) are not generallyavailable to ordinary users

Using Comments to DescribeDatabase Objects


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Sample Queries on the DD

Can a particular user create a table with aparticular name, or has s/he already usedthat name?

Which views are based on more than one

base table? Finally, one to show you we have not covered

everything there is to know ... How much storage space is still free in the entire

database? select sum(f.length*ts.blocksize)

from sys.ts$ ts, sys.fet$ f

where ts.ts# = f.ts#;


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grant statementconnect, dba, resource

Several versions of grant statement

connect: allows new users to have access to Oracle

grant connect to jeff

identified by pwxx4r; resource: allows users to create their own tables

with all privileges (see later) on those tables

grant resource to veda, greenthing;

/* Assumes veda and greenthing exist dba: execute all commands on all database objects

grant dba to mom, dick, mary

identified by dad, ehsg, plymouth;


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grant StatementTable Privileges

Allows owner of a table to control access by other

database users to data in the tables

Types of access include

select: allows users to select from specifiedtable

insert, delete, update, index, alter

references: allows user to define foreign keys

on specified table all: allows user all privileges specified above

with grant option clause allows recipient to

pass the privilege on


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grant insert on orders to paulwith grant option;

grant insert, delete, update

on customers to marilyn;

grant update (quantity)

on products

to anil;

grant select on agents to public;/* Provides every user the

privilege */

grant StatementTable Privileges


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All table privileges are stored in a table calledTABAUTH$ with primary key SEQUENCE#

Update privileges on columns are stored inCOLAUTH$

revoke statement withdraws privilegespreviously granted (connect, dba, resource, tableprivileges)

revoke dba from dick;

revoke resource from greenthing; revoke delete on customers frommarilyn;

revoke select on agents from public;

grant and revoke Statements

12.Data Dictionary

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