access control list (ACL) A list associated with a file that contains information about which users or groups have permission to access or modify the file.

account operator Windows NT Server operator who manages user accounts.

active data in memory Data being read or written to.

Active Directory Single, network-based storage hierarchy based on X.500 standards and protected by ACLs.

ad hoc name Name based on the OPENROWSET function.

adjective phrasing English Query phrasing that expresses an adjectival relationship, for example, "books are popular."

aggregation Precomputed higher-level (rolled up) value that summarizes low-level (detail) data in a dimension.

alert Microsoft SQLServerAgent service definition matching one or more SQL Server events and a response, should those events occur.

analysis server Server providing the core computational functionality of OLAP services.

article Any grouping of data to be replicated.

auditing The process an operating system uses to detect and record security-related events, for example, an attempt to create, access, or delete objects such as files and directories.

Authentication In a multiuser or network operating system, the process by which the system validates a user's logon information. A user's name and password are compared against an authorized list; if the system detects a match, access is granted to the extent specified in the permission list for that user.

Authenticode A cryptographic feature of Microsoft Internet Explorer.

automatic parameter Parameter resulting from caching a plan created for dynamic SQL and turning the constants into parameters.


backward compatibility mode Mode in which a SQL Server 7.0 application or database functions as it did in SQL Server 6.x.

bidirectional merge replication Merge replication in which updated records on the mobile client are copied to the server and vice versa.

biometric authentication Authentication provided by devices such as fingerprint or retinal scanners.


Certificate Management Process through which public and private encryption keys are securely and reliably managed by a Certification Authority.

chained transactions Sybase System 10 transactions that have implicit starting points but must be explicitly committed.

clock algorithm Data access control method used by SQL Server 7.0.

clustered index Index in which the order of the values is the same as the order of the data in the table.

COM The extension reserved by MS-DOS for a type of executable binary (program) file limited to a single 64-KB segment.

configuration Alternative set of indexes.

console tree Tree of categories and objects relevant to a particular server. This tree is found on the left pane of MMC.

context switching A type of multitasking; the act of turning the central processor's "attention" from one task to another, rather than allocating increments of time to each task in turn.

convergence Transactional consistency level in which all sites can work freely in a disconnected manner; when all the nodes have synchronized, all sites converge to the same value.

correlated queries Nested queries. (See nested queries.)

cost threshold value Value used to assess the first potential operation plan. If the latter's value is less than cost threshold, no further cost optimization takes place and execution begins immediately.

cost-based query optimizer Query optimizer that chooses a SQL Server procedural plan on a cost-effective basis.

covered query Query handled by an explicitly declared covering index or index intersection.

covering index Nonclustered index built upon all of the columns required to satisfy a SQL Server query, both in the selection criteria and in the WHERE clause.

CryptoAPI Microsoft's cryptographic application programming interface (APIs); a set of software libraries with high-level APIs that manage the details of key management, formatting, and cipher algorithms.

cryptography Security feature that protects the privacy and integrity of data, especially data in transit across a network.

cube Information container in the OLAP data model, for example, the cube of sales information. (See dimension; hierarchy; measure; level; virtual cube.)

Custom Conflict Resolution Merge replication conflict resolution method that makes use of custom resolvers.

custom resolver A COM-object or stored procedure written to the public resolver interface and invoked during reconciliation by the Merge Agent to support business rules.


DA controller Internal SCSI controllers that connect all of the internal disk drives within the Symmetrix storage system into the 4-GB internal cache.

Data Access Object (DAO) Connectivity tool designed for desktop access to data and based on the Microsoft Jet database engine technology.

data consumer Any component that needs to access data from the OLE DB provider.

data explosion Dramatic increase of the volume of stored data due to excessive preaggregation.

data mart A scaled-down version of a data warehouse that is tailored to contain only information likely to be used by the target group. (See dependent data mart; independent data mart.)

data page Page containing all the data associated with the rows of a table, except text and image data.

data provider OLE DB component that owns the data it exposes to the outside world.

data sparsity Relative lack of data values in a cube, which can waste data storage space and system resources.

data warehouse Subject-oriented, integrated, time-variant, non-volatile store of data collected from other systems that becomes the foundation for decision support and data analysis.

Decision Support Objects Object model allowing programmatic access to administrative functions in the OLAP Services Analysis Server.

default result sets Set-based operations.

defined table Table in which the number and types of columns are either known in advance or specified as part of the query.

degree of parallelism Actual number of threads used by a parallel query.

dependent data mart Data mart containing a subset of enterprise-wide data.

Desktop OLAP (DOLAP) Enables the user to analyze a data slice multidimensionally while disconnected from the corporate network, for example, a traveling sales manager viewing revenue summary for a particular region.

details pane Right pane of MMC detailing a selected item on the console tree.

dimension Descriptive category in a cube within the data warehousing paradigm, for example, the dimensions of time, geography, product, and so on in a sales cube.

dirty page Any buffer cache page modified after being brought into the buffer cache.

Distributed COM (DCOM) The version of Microsoft's Component Object Model (COM) specification that stipulates how components communicate over Windows-based networks. It permits the distribution of different components for a single application across two or more networked computers and allows an application to run distributed across a network so that the distribution of components is not apparent to the user.

Distributed Password Protocol A password-based authentication protocol.

distributed query Any SELECT, INSERT, UPDATE, or DELETE statement that references tables and rowsets from one or more external OLE DB data sources.

Distribution Agent Agent that moves the transactions and snapshot jobs held in distribution database tables to Subscribers.

DNA architecture Windows Distributed interNet Applications architecture.

drive pool methodology A technique for creating disk I/O parallelism.

DTS Data Pump High-speed, in-process COM server that moves and transforms OLE DB rowsets between heterogeneous data stores.

DTS package Complete description of all the work to be performed as part of the transformation process.

DTS step object Object coordinating the flow of control and execution of tasks in the DTS package.

dynamic locking Low-cost locking determined at run time by the storage engine and query processor based on the characteristics of the schema and query.


enabling technology Set of software libraries that encapsulates certain algorithms or procedures, which the operating system makes available to other applications and system services.

enterprise data warehouse Data warehouse containing enterprise-wide data for consolidated data analysis.

exchange operator Operator in a query execution plan that provides process management, data redistribution, and flow control.

exclusive lock Lock preventing concurrent transactions from updating the same resource at the same time. (See update lock.)

explicit transaction Transaction that issues BEGIN TRANSACTION, COMMIT or ROLLBACK statements.

extended memory size option SQL Server 7.0 Enterprise Edition memory configuration parameter that indicates the number of megabytes of memory to use as a disk cache in addition to the conventional buffer pool.

extent Basic unit in which space is allocated to tables and indexes. An extent is a contiguous group of eight pages, or 64 KB.


fact Numeric data that is the core of what is being analyzed.

FASMI test Refinement of Codd's definition of OLAP, stating that OLAP applications should deliver Fast Analysis of Shared Multidimensional Information.

fiber Windows NT lightweight thread scheduled within a single OS thread.

file content search Type of search that supports property textual searches and full-text searches, and can incorporate such searches into a query that includes relational operations against database data.

file grow Automatic space allocation to a file to prevent logs or databases from running out of space.

file shrink Automatic size reduction of a file carried out by moving rows from pages at the end of a file to pages allocated earlier in the file.

firewall A security system intended to protect an organization's network against external threats, such as hackers, coming from another network, such as the Internet.

first-wins conflict resolution Merge replication conflict resolution method in which the winner is the one who first submitted the change.

flattening Conversion of nested queries into semi-joins.

FREETEXT predicate Predicate used to determine whether values in full-text registered columns reflect the meaning, rather than the exact words, specified in the predicate.

full-text catalog Entity holding a collection of full-text indexes.

full-text search A search for one or more documents, records, or strings based on all of the actual text data rather than on an index containing a limited set of keywords.


global temporary table Temporary table that is visible to all sessions.

group Security administrative unit within the Windows NT operating system that contains Windows NT user accounts or other groups. Privileges can be specified for the group, and each member will have those privileges. (See role.)

GUID Globally unique identifier. In the Component Object Model (COM), a 16-byte code that identifies an interface to an object across all computers and networks.


hard page fault Memory management problem in which Windows goes to disk to resolve memory references.

hash To be mapped to a numerical value by a transformation known as a hashing function. Hashing is used to convert an identifier or key, meaningful to a user, into a value for the location of the corresponding data in a structure, such as a table.

hash buckets SQL Server 7.0 system configuration parameter consisting of a prime number used as input into a memory-hashing algorithm.

hash join Join that hashes input values, based on a repeatable randomizing function, and compares values in the hash table for matches.

hash team Technique consisting of taking advantage of similar operations across multiple phases.

heap Table that has nonclustered index(es).

heap page Nonclustered index page.

heterogeneous data Data stored in a data store other than SQL Server.

hierarchy Range of levels of data detail within a data warehousing dimension, for example, years, months, and days, in the time dimension.

homogeneous data Data currently stored in SQL Server.

hot plug Ability of a RAID controller to provide a failed drive replacement while remaining online.

hot spot Area on a disk where many queries try to read or write data at the same time, which creates a disk I/O bottleneck.

Hybrid OLAP (HOLAP) Combines the best features of the ROLAP and MOLAP architectures: superior performance and extensive scalability.

hyper-volume The logical division of an EMC hard disk drive.


immediate guaranteed consistency Transactional consistency level in which all participating sites are guaranteed to have the same data values at the same time, and the data is in the state that would have been achieved had all the work been done at the publishing site.

impersonation Process in which remote server applications can assume the identity of your user account.

implicit transaction Transaction that has an implicit starting point but must be explicitly committed.

incremental repopulation Writing only data changes to the table since the last population.

independent data mart Data mart containing data coming directly from the operational data sources.

Index Allocation Map (IAM) SQL Server 7.0 method of recording the location of extents.

index intersection Process in which the query processor considers multiple indexes from a given table, builds a hash table based on them, and uses the hash table to reduce I/O for a query.

index join A variation on index intersection, consisting of joining multiple indexes to form a covering index.

index page Page that contains only data from columns that comprise a particular index.

index provider Provider that supports and exposes indexes according to OLE DB and allows index-based lookup of base tables.

indexing components Components that manage the initial population and subsequent updating of the full-text indexes.

inflectional forms Changes undergone by a word to reflect change of number, gender, voice, mood, and so on, for example, "child" and "children", "drive," "drives," "drove," "driving," and "driven."

inflectional stem A word's basic inflectional form, from which all the inflectional forms derive; for example, "do" is the stem of "does," "did," and "done."

insertion hot spots Hot spot created by inserting data in the same disk area, for example, the end of a busy table.

integrity Completeness and accuracy of data stored in a computer, especially after it has been manipulated in some way.

intent lock Lock indicating that SQL Server is attempting to acquire a shared or exclusive lock on some of the resources lower in the hierarchy.

interesting ordering Avoiding sort operations by keeping track of the ordering of intermediate results that move from operator to operator.

interface Object consisting of a collection of methods that a client application can call, which are assembled and exposed to the system in the same way, regardless of the language used to create the object.

inter-query parallelism Ability to assign different queries to different processors.

intra-query parallelism Ability to break a single query into multiple subtasks and execute them on multiple processors in an SMP computer.


join Referencing together in a query multiple tables from a relational database.


key A row lock within an index.

key management The process of distributing keys between sender and receiver.


last checked Value stored in each buffer representing the last time the clock came by to check on this buffer.

last touched Value stored in each buffer page representing the last time this buffer page was active.

latent guaranteed consistency Transactional consistency level in which all participating sites are guaranteed to have the same data values that were achieved at the publishing site at some point in time.

leaf node Lowest level of the index tree of a clustered index; storage location of the index entry of a nonclustered index.

level Rung on the hierarchical ladder of a dimension.

linguistic search Word search, phrase search, or prefix search.

linked server-based name Four-part name of the form <linked-server>.<catalog>. <schema>.<object>.

local temporary table Temporary table that is visible only in the current session.

log file Operating system file that holds all the transaction log information used to recover a database.

Log Reader Agent Agent that moves transactions marked for replication from the transaction log on the Publisher to the distribution database.

loose consistency Latent guaranteed consistency.


major entity Semantic entity normally used in English Query to correspond to an entire table.

mallet Traditional name of the nefarious intermediary blocked by cryptography.

measure Quantitative value found in a cube, for example, dollar sales, unit sales, and so on in a sales cube.

Merge Agent Agent that moves and reconciles incremental data changes that occurred after the initial snapshot was created.

merge join Join that simultaneously passes over two sorted inputs to perform inner joins, outer joins, semi-joins, intersections, and unions.

merge replication Mode of replication in which Publishers and Subscribers can work independently and reconnect periodically to merge their results, with automatic conflict resolution.

message digest Small value (usually 16 bytes) produced by a hashing algorithm from an arbitrarily long stream of data.

metadata Descriptive information about software components and their relationships.

minor entity English Query semantic entity associated with a major entity. (See name; trait.)

mirroring Method of fault tolerance to hard disk failure implemented by writing the same information onto two sets of drives.

mixed extent Extent that allows allocation of a single page to a small table or index.

model Database used as the template for all the databases created on the SQL Server system.

MSSQLServer service Primary service responsible for SQL Server.

multiphase optimization Form of optimization using a cost threshold value to prevent over-optimization.


name Type of English Query minor entity that indicates how its associated major entity is identified in questions and statements, for example, "book" refers to the major entity Books table.

name phrasing English Query phrasing that expresses a name relationship, for example, "author names are the names of authors."

nested queries Queries that are created on top of other queries in a nested fashion.

nested views Views that are created on top of other views in a nested fashion.

Network Library Microsoft SQL Server Net-Library used by the client to connect to the aliased server.

noise word Extremely common word of no interest to a full-text search, for example, "a," "but," and "the."

non-SQL Command Providers Provider that supports the Command object and its mandatory interfaces but does not support a SQL standard dialect recognized by SQL Server.

nonclustered indexes B-trees formed out of 8-KB index pages.

nonleaf level Upper part of an index B-tree structure.

nonrelational data Data not stored in relational databases, for example, audio and video clips and e-mail messages.


one-computer upgrade Upgrading to SQL Server 7.0 on your existing hardware.

online RAID expansion RAID feature allowing disks to be added dynamically to a physical RAID array while online, as long as there are hot-plug slots available.

Open Database Connectivity (ODBC) A C/C++ API designed to target different sources from the same source code by substituting different drivers.

Open Information Model Object models for specific types of information, flexible enough to support new information types.

over-optimization Occurs when the query optimizer uses more resources to determine the best plan than are required to execute the plan.

Open Databases Configuration parameter in SQL Server version 6.5 and earlier consisting of the number of SQL Server databases allowed to be active at any one time.

Open Objects Configuration parameter consisting of the number of objects SQL Server allows to have actively open at any point in time.

optimistic concurrency control Form of concurrency control that does not place shared locks on tables.


page Fundamental unit of data storage in SQL Server, consisting of 8 KB.

page chain Sequence of pages in which each page has a pointer to the next page holding data for the table.

page splitting Creation of two nonsequential pages from one page lacking the space to accept new data that must be inserted into the page because of the logical ordering of data defined in that page.

parallel data scanning Reading sequential data in parallel.

parallel query Parallel execution of a single query across multiple processors.

parallel utilities Utilities run in parallel.

parameterized query Query in which the application identifies the parameters.

parity Error-checking procedure in which the number of 1s must be the same—either even or odd—for each group of bits transmitted without error. Method of fault tolerance.

partial preaggregation Optimal preaggregation that computes only the optimum set of aggregations from which all other aggregations can be derived at run time.

partitioned cube Logical cube that is spread over multiple physical cubes and even separate physical servers.

PASSFILT Enabling technology that lets an administrator install a trusted program that is called every time a user changes a password.

permissions validation stage Security stage that controls the activities the user is allowed to perform in the SQL Server database.

Personal Information Exchange A protocol that securely transfers the contents of a P-Store from one location to another.

pessimistic concurrency control Form of concurrency control that places shared locks on tables.

phrase search Search for two or more words following one another immediately, after noise words have been disregarded.

phrasing English Query syntactical expression of a relationship. (See adjective phrasing; name phrasing; preposition phrasing; subset phrasing; trait phrasing; verb phrasing.)

pool methodology See drive pool methodology.

preaggregation The precomputing of aggregations.

prefetch hint Message from the query processor to the storage engine listing which records the query processor will soon need.

prefix Any character or group of characters used to specify a prefix search.

prefix search Search for all words that begin with a given prefix, for example, "geo*" finds "geophysics" and "geography."

preposition phrasing English Query phrasing that expresses a prepositional relationship, for example, "publishers are in cities."

primary file Starting point of the database; contains the pointers to the rest of the files in the database.

priority-based conflict resolution Merge replication conflict resolution method in which every publication is assigned a priority number so that in case of conflict, the publication with the highest number wins.

Private Communication Technology (PCT) An improved version of Secure Sockets Layer.

processor affinity Association between a processor and a thread.

property textual search Search done on document properties such as author, subject, type, word count, printed page count, and time last written.

Protected Store (P-Store) A set of software libraries that allows applications to fetch and retrieve security and other information from a personal storage location, hiding the implementation and details of the storage itself.

proximity search A search for words or phrases found near one another, but not following one another immediately even after noise words are disregarded.

public key encryption Asymmetric scheme that uses a pair of keys for encryption: the public key encrypts data, and a corresponding secret key decrypts it. For digital signatures, the process is reversed: the sender uses the secret key to create a unique electronic number that can be read by anyone possessing the corresponding public key, which verifies the message is from the sender.

publication Collection of one or more articles.

Publisher Server that makes data available for replication to other servers.

pull subscription Subscription in which the Subscriber asks for periodic updates of all changes at the Publisher.

push subscription Subscription in which the Publisher propagates the changes to the Subscriber without a specific request from the Subscriber.


query cost Estimated elapsed time, in seconds, required to execute a query on a specific hardware configuration.

query execution Major phase in query processing consisting of executing the plan chosen during query optimization.

query governor SQL Server 7.0 feature that prevents a query from running if its query cost is greater than an administrator-specified upper cost limit.

query optimization Major phase in query processing consisting of choosing the fastest execution plan.

query processor Major SQL Server component that accepts, selects, and then executes the plan chosen for executing the syntax.


random I/O Form of disk I/O in which data is read in random order.

recovery Restoration of lost data or the reconciliation of conflicting or erroneous data after a system failure. Recovery is often achieved using a disk or tape backup and transaction logs.

referential integrity The way in which an RDBMS manages relationships between tables.

relationship English Query semantic relationship between entities, for example, "publishers publish books" is a relationship between the major entities "publishers" and "books." (See phrasing.)

Remote Access Service (RAS) Windows software that allows a user to gain remote access to the network server by using a modem.

Remote Data Objects (RDO) Object-oriented data access tool with no native file format of its own. RDO can be used only with databases complying with the most recent ODBC standards.

Remote Data Services (RDS) Client-side component that interfaces with ADO and provides cursors, remote object invocation, and explicit and implicit remote recordset functionality such as fetch and update.

remote table Table stored in an OLE DB data source and external to the server running SQL Server executing the query.

Replication Monitor Component of a Distributor enabling a member of the sysadmin fixed server role to view the status of replication agents and troubleshoot potential problems at the Distributor.

role Security administrative unit within SQL Server that contains SQL Server logins, Windows NT logins, groups, or other roles. (See group.)

rowset A tabular object used by OLE DB to expose its data.


sandbox Scope of a Java applet.

search engine Program that searches for key words in documents or in a database.

secure channel Communications link that has been protected against unauthorized access, operation, or use by means of isolation from the public network, encryption, or other forms of control.

Secure DCOM DCOM options that automatically use SSPI authentication and message encryption.

Secure RPC RPC options that automatically use SSPI authentication and message encryption.

Secure Sockets Layer (SSL) Proposed open standard developed by Netscape Communications for establishing a secure communications channel to prevent the interception of critical information.

security principals Users and groups of users, from the point of view of the SQL Server 7.0 security system architecture.

Security Support Provider A library that manages a particular authentication or cryptographic scheme.

selectivity Property that relates to how many rows are typically identified by a key value. A unique key value has high selectivity; a nonunique key value (for example, one found in 1,000 rows) has poor selectivity.

semantic entity English Query entity used to establish semantic relationships between tables, table elements, and so on, allowing the user to type database queries in English language phrases, which are then translated into SQL statements. (See major entity; minor entity.)

sequential I/O Form of disk I/O in which data is read in the same order as it is stored on the disk.

serial execution plan Execution plan used by a nonparallel query.

server alias Label by which the entry will be referenced at connect time.

service component Logical OLE DB object that encapsulates a piece of DBMS functionality, for example, query processors, cursor engines, or transaction managers.

shared lock Lock that allows concurrent transactions to read a resource.

simple table provider Provider that exposes the opening of a rowset against a base table through the IOpenRowset interface.

simulated configuration Configuration that is not actually created and is used only to estimate the costs if it were created.

singleton SELECT SELECT statement that returns one row based on the criteria defined in the WHERE clause of the statement.

site autonomy State of affairs in which all sites operate independently.

Snapshot Agent Agent that prepares the schema and initial data files of published tables and stored procedures, stores the snapshot on the Distributor, and records information about the synchronization status in the distribution database.

snapshot replication Type of replication that takes a picture, or snapshot, of the published data in the database at one moment in time and does a total refresh of the Subscriber data.

soft page fault Memory management problem in which an application requests memory pages still inside RAM but outside of the application's Working Set.

sort pages Amount of memory allocated per user for sorting operations in SQL Server 6.5.

spindle Axle for mounting a disk or reel of magnetic tape.

spoofing Practice of making a transmission appear to come from an authorized user.

star index Multicolumn index on a star-schema's fact table used in conjunction with the Cartesian product strategy.

star schema Type of database schema designed to allow a user to intuitively navigate information in the database.

static structures SQL Server 6.5 preallocation of SQL Server memory to SQL Server components such as user connections, locks, open objects and worker thread.

storage engine Major SQL Server component that writes data to and reads data from the disk. It manages records, controls concurrency, and maintains log files.

storage location Position at which a particular item can be found—either an addressed location or a uniquely identified location on a disk, tape, or similar medium.

stored procedure Procedure that is actually stored within a database.

stored procedure cache SQL Server 6.5 fixed segment of memory based on the procedure cache sp_configure parameter.

stored procedure percent SQL Server 6.5 configuration parameter that sets what percentage of the available memory left goes to procedure cache.

Subscriber Server that stores replicas and receives updates from a publisher.

subset phrasing English Query phrasing that expresses a subset relationship, for example, "some books are bestsellers."

syntax-based query optimizer Query optimizer that creates its SQL procedural plan on the basis of the exact syntax of the query and the order of the clauses within the query.

system integrity Security feature that ensures the underlying security software cannot be tampered with.


temporary table Table that creates a snapshot of data for a connected user's session.

text search catalog Catalog in which Index Services stores indexes and property values.

thread In programming, a process that is part of a larger process or program.

tight consistency Immediate guaranteed consistency.

torn page Page that is written only partially, due to a power failure or another problem.

torn page detection Detection of incomplete I/O.

trait Type of English Query minor entity that identifies what its associated major entity has; for example, "books have titles," "books have authors." A trait is a kind of relationship. (See relationship.)

trait phrasing English Query phrasing that expresses a trait relationship, for example, "books have royalties."

Transact-SQL Simple programming language that provides basic conditional processing and simple repetition control, included in Microsoft SQL Server.

transaction log File that records transactional changes occurring in a database, providing a basis for updating a master file and establishing an audit trail.

Transport Layer Security An upcoming Internet standard that merges SSL and the ideas in PCT.

transactional consistency State of affairs in which all sites are guaranteed to have the same data values at the same time.

transactional replication Replication method in which transactions (INSERT, UPDATE, or DELETE statements) executed on one computer are replicated to another computer.

transformation Sequence of procedural operations that is applied to the information in a data source before it can be stored in the specified destination.

trigger Action that causes a procedure to be carried out automatically when a user attempts to modify data.

trust Unilateral access of the accounts of one domain to another domain.

trusted path Windows NT security feature that prevents spoofing.

two-computer upgrade Upgrading to SQL Server 7.0 on a new computer.

two-phase commit Process that ensures transactions applying to more than one server are completed on either all servers or none.


uniform extent Extent owned by a single object; all pages in the extent can be used only by the owning object.

universal server approach Approach in which all data must exist in a single repository and must be accessed using a single access language.

update lock Lock allowing only one transaction at a time to update a resource, thus preventing the deadlocks due to concurrent attempts to obtain an exclusive lock.

user-defined filegroup Filegroup defined by the user.

user rights Special capabilities that administrators assign to accounts that can use a given computer.


verb phrasing English Query phrasing that expresses a verbal relationship, for example, "authors write books."

view Logical table created through the specification of one or more relational operations on one or more tables.

virtual cube Cube consisting of two or more physical, logical, or partitioned cubes linked at query time along one or more common dimensions.

virtual directory Directory that references one or more physical directories and, optionally, other virtual directories.

virtual log file Logical segment of a log file; unit of truncation for the transaction log.

virtual memory Memory that appears to an application to be larger and more uniform than it is.


width threshold Limit beyond which the Cost Evaluation module of the Index Tuning Wizard ceases to consider wider indexes.

worker thread Windows operating system threads used to service batches of SQL Server commands submitted to the database server.

wrapper DLL DLL that intercepts external library function calls made to an application to control the application or process that instantiated the DLL.