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abstract classes   
Templates used only to derive new Structural classes. Abstract classes cannot be instantiated in the directory.

access control   
A security mechanism that determines which operations a user, group, service, or computer is authorized to perform on a computer or on a particular object, such as a file, printer, registry subkey, or directory service object. See also group; object; permission; registry.

access control list (ACL)   
A list of security protections that apply to an entire object, a set of the object’s properties, or an individual property of an object. There are two types of access control lists: discretionary and system. See also object.

ACL   
See definition for access control list (ACL).

Active Directory   
The Windows-based directory service. Active Directory stores information about objects on a network and makes this information available to users and network administrators. Active Directory gives network users access to permitted resources anywhere on the network using a single logon process. It provides network administrators with an intuitive, hierarchical view of the network and a single point of administration for all network objects. See also directory partition; directory service; domain; forest; object.

Active Directory Service Interfaces (ADSI)   
A directory service model and a set of Component Object Model (COM) interfaces. ADSI enables Windows applications and Active Directory clients to access several network directory services, including Active Directory. ADSI is supplied as a software development kit (SDK). See also Active Directory; Component Object Model (COM); directory service.

ActiveX   
A set of technologies that allows software components to interact with one another in a networked environment, regardless of the language in which the components were created.

Address Resolution Protocol (ARP)   
In TCP/IP, a protocol that uses broadcast traffic on the local network to resolve a logically assigned Internet Protocol version 4 (IPv4) address to its physical hardware or media access control (MAC) layer address.

In asynchronous transfer mode (ATM), ARP is used two different ways. For classical IPv4 over ATM (CLIP), ARP is used to resolve addresses to ATM hardware addresses. For ATM LAN emulation (LANE), ARP is used to resolve Ethernet/802.3 or Token Ring addresses to ATM hardware addresses.

See also asynchronous transfer mode (ATM); Internet Protocol (IP); IP address; packet; Transmission Control Protocol/Internet Protocol (TCP/IP).

administrative credentials   
Logon information that is used to identify a member of an administrative group. Groups that use administrative credentials include Administrators, Domain Admins, and DNS Admins. Most system-wide or domain-wide tasks require administrative credentials. See also Administrators group; group.

Administrators group   
On a local computer, a group whose members have the highest level of administrative access to the local computer. Examples of administrative tasks that can be performed by members of this group include installing programs; accessing all files on the computer; auditing access control; and creating, modifying, and deleting local user accounts.

In an Active Directory domain, a group whose members have the highest level of administrative access in the domain. Examples of administrative tasks that can be performed by members of this group include setting domain policy; assigning and resetting domain user account passwords; setting up and managing domain controllers; and creating, modifying, and deleting domain user accounts.

See also access control; Active Directory; auditing; domain; domain controller; group; object.

ADSI   
See definition for Active Directory Service Interfaces (ADSI).

ADSI provider   
COM objects that implement ADSI for a particular namespace (for example, an LDAP namespace such as Active Directory).

agent   
An application that runs on a Simple Network Management Protocol (SNMP) managed device. The agent application is the object of management activities. A computer running SNMP agent software is also sometimes referred to as an agent.

aggregation   
A composition technique for implementing component objects in which a new object can be built by using one or more existing objects that support some or all of the new object’s required interfaces.

American Standard Code for Information Interchange (ASCII)   
A standard single-byte character encoding scheme used for text-based data. ASCII uses designated 7-bit or 8-bit number combinations to represent either 128 or 256 possible characters. Standard ASCII uses 7 bits to represent all uppercase and lowercase letters, the numbers 0 through 9, punctuation marks, and special control characters used in U.S. English. Most current x86-based systems support the use of extended (or “high”) ASCII. Extended ASCII allows the eighth bit of each character to identify an additional 128 special symbol characters, foreign-language letters, and graphic symbols.

Anonymous access   
An authentication mechanism by which users who are able to connect to an Internet site without credentials are assigned to the IUSR_ComputerName account and granted the access rights that are assigned to that account. See also access control; Anonymous authentication; authentication.

Anonymous authentication   
An authentication mechanism that does not require user accounts and passwords. Anonymous authentication grants remote users the identity IUSR_ComputerName. Anonymous authentication is used on the Internet to grant visitors restricted access to predefined public resources. See also Anonymous access; authentication.

Anonymous FTP authentication   
A protocol that makes it possible for a user to retrieve documents, files, programs, and other archived data from anywhere on the Internet without having to establish a logon name and password.

apartment-threaded   
A threading model in which each method of a component will execute on a thread that is associated with that component. See also multithreaded apartment (MTA); single-threaded apartment (STA).

API   
See definition for application programming interface (API).

application   
A computer program, such as a word processor or electronic spreadsheet, or a group of Active Server Pages (ASP) scripts and components that perform such tasks.

application isolation   
The separation of applications by process boundaries that prevent the applications from affecting one another. Application isolation is configured differently for each of the two Internet Information Services (IIS) isolation modes. See also IIS 5.0 isolation mode; worker process isolation mode.

application pool   
A grouping of one or more URLs served by a worker process.

application programming interface (API)   
A set of routines that an application uses to request and carry out lower-level services performed by a computer’s operating system. These routines usually carry out maintenance tasks such as managing files and displaying information.

application root   
The root directory for an application. Al