Glosario de Bases de Datos Sybase, "D"

See buffer cache

The process of setting up databases and creating database objects such as tables, indexes, rules, defaults, procedures, triggers, and views. See also source text .

The system tables that contain a description of each database object and how it is structured.

The correctness and completeness of data within a database.

Adding, deleting, or changing information in the database with the insert, delete, and update commands.

The act of requesting data from the database and receiving the results. See also query .

A subject-oriented information store specifically designed for decision support and analytical processing. A data warehouse contains large amounts of information used by managers, strategic marketers, and merchandisers to help them understand and predict market trends and make crucial business decisions. The information in a data warehouse is not usually modified by the people who use it. See also database .

See relational database .

The tasks involved in maintaining, designing, implementing changes to, tuning, and expanding a database. See also system administration .

A device dedicated to the storage of the objects that make up databases.

See table .

A characteristic of a database evidenced by the database being both valid and complete. Database integrity consists of two complementary components: validity, which guarantees that all false information is excluded from the database, and completeness , which guarantees that all true information is included in the database. See also integrity constraints .

One of the components of a database: table, column, view, index, procedure, trigger, default, or rule. See also object .

A user who creates a database object .

The creator of a database. The Database Owner has control over all the database objects in that database. The login name for the Database Owner is "dbo."

Specifies what kind of information each column will hold and how the data will be stored. Datatypes include char, int, money , and so on. Users can construct their own datatypes based on the Adaptive Server system datatypes.

A function that is used to convert expressions of one datatype into another datatype, whenever these conversions are not performed automatically by Adaptive Server.

The hierarchy that determines the results of computations using values of different datatypes.

A function that displays information about dates and times, or manipulates date or time values. The date functions include getdate, datename, datepart, datediff, and dateadd.

Parts of a date, such as day, month, or year, recognized by the Transact-SQL date functions.

Database Management System. The Adaptive Server DBMS component performs query processing and transaction management for the current task. For example, the DBMS parses, compiles, and executes SQL statements and returns any results.

See Database Owner .

A deadlock occurs when two or more user processes each have a lock on a separate page or table and each wants to acquire a lock on the other process's page or table. The transaction with the least accumulated CPU time is killed and all of its work is rolled back.

A database system that supports queries involving large amounts of data. Commonly used to make business decissions. DSS queries typically access entire tables or large portions of tables, involve joins between many tables, and return summaries of large result sets. DSS applications are often run on a scheduled basis; for example, to produce the same report at the close of every business day. See also data warehouse .

The option chosen by the system when no other option is specified.

Specifies the default value for a column in the create table statement.

The database that users connect to when they log in.

For a user, the language that displays that user's prompts and messages, set with sp_modifylogin or the language option of the set command. For Adaptive Server, the language used to display prompts and messages for all users unless a user chooses a different language.

An update operation that takes place in two steps. First, the log records for deleting existing entries and inserting new entries are written to the log, but only the delete changes to the data pages and indexes take place. In the second step, the log pages are rescanned, and the insert operations are performed on the data pages and indexes. See also direct update .

See source text .

The number of worker processes that the optimizer chooses to execute the query in parallel. The degree of parallelism depends on both the upper limit of parallelism for the query and the level of parallelism suggested by the optimizer.

A type of direct update operation. The row is deleted from its original location, and inserted at a new location.

Object names enclosed in double quotes that avoid certain restrictions on object names.

A demand lock prevents any more shared locks from being set on a table or data page. Any new shared lock request has to wait for the demand lock request to finish.

The average fraction of all the rows in an index that have the same key value.
Density is 1 if all of the data values are the same and 1/N if every data value is unique.

Data is logically dependent on other data when master data in one table must be kept synchronized with detail data in another table in order to protect the logical consistency of the database.

Data that logically depends on data in another table. For example, in the pubs2 database, the salesdetail table is a detail table. Each order in the sales table can have many corresponding entries in salesdetail. Each item in salesdetail is meaningless without a corresponding entry in the sales table.

Software such as PowerBuilder that helps you build specialized GUI applications for accessing SQL Server databases.

Any piece of disk (such as a partition ) or a file in the file system used to store databases and their objects. See also database device .

The action of reading to or writing from a database device .

An update operation that takes place in a single step, that is, the log records are written and the data and index pages are changed. Direct updates can be performed in three ways: in-place update , on-page update , and delete/insert direct update . See also deferred update .

Occurs when one transaction modifies a row, and then a second transaction reads that row before the first transaction commits the change. If the first transaction rolls back the change, the information read by the second transaction becomes invalid.

Restrict your access to objects based on your identity and/or your group membership. The controls are discretionary in the sense that a user with a certain access permission is capable of passing that permission onto any other user (such as with the grant command). See also permissions .

Disk allocation pieces are the groups of allocation units from which Adaptive Server constructs a new database file. The minimum size for a disk allocation piece is one allocation unit .

The process of preparing a database device or file for Adaptive Server use. After the device is initialized, it can be used for storing databases and database objects. The command used to initialize a database device is disk init.

A duplicate of a Adaptive Server database device. All writes to the device being mirrored are copied to a separate physical device, making the second device an exact copy of the device being mirrored. If one of the devices fails, the other contains an up-to-date copy of all transactions. The command disk mirror starts the disk mirroring process.

The number of significant binary digits offered by the default display format for real and float values. Internally, real and float values are stored with a precision less than or equal to that of the platform-specific datatypes on which they are built. For display purposes, Sybase real values have 9 digits of precision; Sybase float values, 17.

Dynamic Link Library. Software used by Microsoft Windows and IBM OS/2 to provide services to applications.

ASybase library that provides an interface to an external service provider.

The action of making a backup of an entire database, including the data and the transaction log , which you accomplish with the dump database command. Also, the data that results from this action. See also load .

Interleaving of dump data across several dump volumes.

A single tape, partition, or file used for a database or transaction dump. A dump can span many volumes, or many dumps can be made to a single tape volume.

A dump made while the database is active.

A worktable built by Adaptive Server for the resolution of queries using or . As each qualifying row is retrieved, its row ID is stored in the worktable. The worktable is sorted to remove duplicates, and the row IDs are joined back to the table to return the values.