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Cytat
Do celu tam się wysiada. Lec Stanisław Jerzy (pierw. de Tusch-Letz, 1909-1966)
A bogowie grają w kości i nie pytają wcale czy chcesz przyłączyć się do gry (. . . ) Bogowie kpią sobie z twojego poukładanego życia (. . . ) nie przejmują się zbytnio ani naszymi planami na przyszłość ani oczekiwaniami. Gdzieś we wszechświecie rzucają kości i przypadkiem wypada twoja kolej. I odtąd zwyciężyć lub przegrać - to tylko kwestia szczęścia. Borys Pasternak
Idąc po kurzych jajach nie podskakuj. Przysłowie szkockie
I Herkules nie poradzi przeciwko wielu.
Dialog półinteligentów równa się monologowi ćwierćinteligenta. Stanisław Jerzy Lec (pierw. de Tusch - Letz, 1909-1966)
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.(We useboth terms in today's presentation.) A data dictionary is a system area within a databaseenvironment that contains information about the ingredients of a database.Datadictionaries include information such as database design, stored SQL code, userstatistics, database processes, database growth, and database performance statistics.The data dictionary has tables that contain database design information, which are populated upon the creation of the database and the execution of Data DefinitionLanguage (DDL) commands such as CREATE TABLE.This part of the system catalogstores information about a table's columns and attributes, table-sizing information,table privileges, and table growth.Other objects that are stored within the datadictionary include indexes, triggers, procedures, packages, and views.User statistics tables report the status of items such as database connectivityinformation and privileges for individual users.These privileges are divided into twomajor components: system-level privileges and object-level privileges.The authority tocreate another user is a system-level privilege, whereas the capability to access a tableis an object-level privilege.Roles are also used to enforce security within a database.This information is stored as well.Day 16 extends what you learned yesterday (Day 15, "Streamlining SQL Statements forImproved Performance").Data retrieved from the system catalog can be used to monitordatabase performance and to modify database parameters that will improve databaseand SQL statement performance.The data dictionary is one of the most useful tools available with a database.It is a wayof keeping a database organized, much like an inventory file in a retail store.It is amechanism that ensures the integrity of the database.For instance, when you create atable, how does the database server know whether a table with the same name exists?When you create a query to select data from a table, how can it be verified that youhave been given the proper privileges to access the table? The data dictionary is theheart of a database, so you need to know how to use it.Users of the Data DictionaryEnd users, system engineers, and database administrators all use the data dictionary,whether they realize it or not.Their access can be either direct or indirect.End users, often the customers for whom the database was created, access the systemcatalog indirectly.When a user attempts to log on to the database, the data dictionaryis referenced to verify that user's username, password, and privileges to connect to thedatabase.The database is also referenced to see whether the user has the appropriateprivileges to access certain data.The most common method for an end user to access thedata dictionary is through a front-end application.Many graphical user interface (GUI)tools, which allow a user to easily construct an SQL statement, have been developed.When logging on to the database, the front-end application may immediately perform aselect against the data dictionary to define the tables to which the user has access.Thefront-end application may then build a "local" system catalog for the individual userbased on the data retrieved from the data dictionary.The customer can use the localcatalog to select the specific tables he or she wishes to query. System engineers are database users who are responsible for tasks such as databasemodeling and design, application development, and application management.(Somecompanies use other titles, such as programmers, programmer analysts, and datamodelers, to refer to their system engineers.) System engineers use the data dictionarydirectly to manage the development process, as well as to maintain existing projects.Access may also be achieved through front-end applications, development tools, andcomputer assisted software engineering (CASE) tools.Common areas of the systemcatalog for these users are queries against objects under groups of schemas, queriesagainst application roles and privileges, and queries to gather statistics on schemagrowth.System engineers may also use the data dictionary to reverse-engineer databaseobjects in a specified schema
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