Glosario de Bases de Datos Sybase, "M,N,O"

MAPI

Messaging Application Programming Interface. An e-mail application programming interface developed by Microsoft. MAPI support for Adaptive Server integrates Adaptive Server with MAPI to provide an interface for sending and receiving data by email rather than through the traditional client/server connection-based facility.

master database

The system database that controls the user databases and the operation of Adaptive Server as a whole. Known as master, it keeps track of such things as user accounts, ongoing processes, and system error messages.

master table

A table that contains data on which data in another table logically depends. For example, in the pubs2 database, the sales table is a master table. The salesdetail table holds detail data that depends on the master data in sales. The detail table usually has a foreign key that joins to the primary key of the master table.

master-detail relationship

A relationship between sets of data where one set of data logically depends on the other. For example, in the pubs2 database, the sales table and salesdetail table have a master-detail relationship. See detail and master table.

matching index scan

A scan using a nonclustered index when the query has a where clause (search argument) on a set of columns, and the columns form a prefix subset of keys on the index. The index is used to position the search at the first matching key, and then scanned forward for additional matches on the specified index key columns. The scan stops at the first row that does not match. Matching index scans are quite fast and efficient. Compare to nonmatching index scan.

mathematical function

A function that returns values commonly needed for operations on mathematical data.

media failure

A media failure occurs when the information on a medium (typically a hard disk drive) becomes unusable.

message number

The number that uniquely identifies an error message.

metadata

Data about data. Metadata is stored in local proxy tables by Component Integration Services. The metadata stored by Component Integration Services represents schemas with information about remote tables.

metadata cache

A reserved area of memory used for tracking information on indexes, objects, or databases. You can configure the size of the metadata caches based on the number of metadata descriptors used by indexes, objects, or databases.

metadata descriptor

A memory data structure that represents the state of an index, an object, or a database while it is in use or cached between uses.

MIME

Multipurpose Internet Mail Extentions. A format for exchanging complex messages through the Internet. Web browsers and servers use MIME types to describe the messages transmitted from the server to the browser.

mirror

See disk mirror.

model database

A template for new user databases. The installation process creates model when Adaptive Server is installed. Each time the create database command is issued, Adaptive Server makes a copy of model and extends it to the size requested, if necessary.

modulo

An arithmetic operator represented by the percent (%) sign that gives the integer remainder after a division operation on two integers. For example, 21 % 9 = 3 because 21 divided by 9 equals 2 with a remainder of 3.

MRU replacement strategy

A caching strategy for table scans and nonclustered index scans. The optimizer chooses this strategy when it determines that the pages need to be accessed only once for a particular query. Instead of adding all of the pages to the MRU/LRU chain, the pages are immediately flushed as soon as the query finishes examining them, and the next page for the query is read into the buffer.

multibyte character set

A character set that includes characters encoded using more than one byte. EUC JIS and Shift-JIS are examples of character sets that include several types of characters represented by multiple bytes in a Japanese language environment.

multiprocessing

Multiple processes that share memory or use some type of synchronized method for passing messages between them are performing multiprocessing.

named cache

See buffer cache .

natural join

A join in which the values of the columns being joined are compared on the basis of equality, and all the columns in the tables are included in the results, except that only one of each pair of joined columns is included.

nested queries

select statements that contain one or more subqueries.

nested select statements

See nested queries .

nonclustered index

An index that stores key values and pointers to data. The leaf level points to data pages rather than containing the data itself.

nonmatching index scan

A scan using a nonclustered index when the search arguments do not form a prefix subset of the index key columns, although they match some parts of the composite key . The scan is performed using the index from the lowest key value to the highest key value, searching for the matches specified in the query. This type of scan is performed on nonclustered indexes when all columns for a table referenced in the query are included in the index. Although cheaper than a table scan, a non-matching index scan is more expensive than a matching index scan .

normalization rules

The standard rules of database design in a relational database management system.

not-equal join

A join on the basis of inequality.

null

A value given to a parameter or option that has no explicitly assigned value. NULL is not equivalent to zero, or to blank. A value of NULL is not considered to be greater than, less than, or equal to any other value, including another value of NULL.

numeric expression

See arithmetic expression .

object

A passive entity that contains or receives information, and that cannot change the information it contains. In Adaptive Server, objects include rows, tables, databases, stored procedures, triggers, defaults, and views. See also database object .

Object Allocation Map (OAM)

One or more pages within a table or an index on a table that contain pointers to the allocation pages for each allocation unit where the object uses space.

object permission

A permissions that regulates the use of certain commands ( data modification commands, plus select, truncatetable and execute commands) to specific tables, views or columns. See also command permission .

ODBC

Open Database Connectivity. The ODBC interface, defined by Microsoft Corporation, is a standard interface to database management systems in the Windows and Windows NT environments.

online transaction processing (OLTP)

Real-time access to and manipulation of data. Commonly used for business applications, for example, a bank customer's transactions at an automatic teller machine. It is characterized by a large number of users that need fast online access to small result sets.

on-page update

A type of direct update operation, performed when the length of the data row changes. The changed data row remains on the same data page, but other rows on the page may move. Contrast to in-place update and delete/insert direct update .

operating system

A group of programs that translates your commands to the computer, so that you can perform such tasks as creating files, running programs, and printing documents.

operating system file

A collection of data named and recognized by the operating system . Adaptive Server data is not stored in operating system files, but can be exported to operating system files by using the bulk copy operation.

Operator

The role required to allow the ability to back up and restore databases on a server-wide basis. See also roles .

operators

Symbols that act on two values to produce a third. See also comparison operators , logical operators , and arithmetic operators .

optimizer

Adaptive Server code that analyzes queries and database objects and selects the appropriate query plan . The Adaptive Server optimizer is a cost-based optimizer. It estimates the cost of each permutation of table accesses in terms of CPU cost and I/O cost.

OR strategy

An optimizer strategy for resolving queries using or and queries using in ( values list) . Indexes are used to retrieve and qualify data rows from a table. The row IDs are stored in a worktable. When all rows have been retrieved, the worktable is sorted to remove duplicates, and the row IDs are used to retrieve the data from the table.

outer join

A join in which both matching and nonmatching rows are returned. The operators *= and =* are used to indicate that all the rows in the first or second tables should be returned, regardless of whether or not there is a match on the join column.

outer query

Another name for the principal query in a statement containing a subquery .

overflow page

A data page for a table with a nonunique clustered index, which contains only rows that have duplicate keys. The key value is the same as the last key on the previous page in the chain. There is no index page pointing directly to an overflow page.

ownership chain

Dependencies of views on other views and/or tables, and of procedures on other procedures, views, and/or tables.