.. glossary::
:sorted:
Adaptive Communication Environment
ACE
ACE is an open source C++ framework that is maintained alongside :term:`TAO` and is extensively used by OpenDDS.
It provides a platform abstraction layer and various utilities such as reactors for event handing.
See :ref:`deps-ace` for more information.
Built-in Topics
BITs
Built-in Topics are :term:`topics <Topic>` that contain meta-information about local and remote :term:`DDS entites <Entity>` and the operational status of OpenDDS.
See :ref:`bit` for more information.
Common Data Representation
CDR
Extended Common Data Representation
XCDR
CDR is a family of binary encoding formats used by OpenDDS to serialize and deserialize :term:`samples <Sample>`.
XCDR is an extended form of CDR defined by the :term:`XTypes` specification.
See :ref:`xtypes--data-representation` for more information.
Common Object Request Broker Architecture
CORBA
CORBA, put simply, is a set of specifications that allows a client to perform remote procedure calls on objects held in a server.
It is separate from :term:`DDS`, but both are published by the :term:`OMG` and make use of :term:`IDL` and :term:`CDR`.
:term:`TAO` is a CORBA implementation that OpenDDS uses for InfoRepo discovery.
See https://www.corba.org/ for more information.
Condition
Conditions are a method of being notified of events from :term:`entities <Entity>`, such a new :term:`sample` being available from a :term:`DataReader`, via a status that can be checked synchronously.
See :doc:`devguide/conditions_and_listeners` for more information.
Data-Centric Publish-Subscribe
DCPS
DCPS is essentially synonymous with :term:`DDS`, but can specifically refer to the API described in the main DDS specification.
Data Distribution Service
DDS
DDS is a specification for exchanging strongly-typed data across a distributed system.
It is essentially synonymous with :term:`DCPS`, but can specifically refer to the main DDS specification.
See :ref:`spec-dds` for more information.
``DataReader``
A ``DataReader`` is an :term:`Entity` that is used to read :term:`samples <Sample>` from a :term:`topic`.
``DataReader``\s are created and managed by :term:`Subscribers <Subscriber>`.
``DataWriter``
A ``DataWriter`` is an :term:`Entity` that is used to write :term:`samples <Sample>` to a :term:`topic`.
``DataWriter``\s are created and managed by :term:`Publishers <Publisher>`.
Discovery
Discovery is the configurable method that :term:`DomainParticipant`\s use to find one another.
See :ref:`dds-introduction--discovery` for more information.
Dispose
When an :term:`instance` is disposed by a :term:`DataWriter`, it means keeping the cached data related to it is no longer necessary.
This is done automatically if the instance is :term:`unregister`\ed and ``autodispose_unregistered_instances`` of :ref:`qos-writer-data-lifecycle` is set to ``true``.
This can also be done manually using ``dispose`` method on ``DataWriter``.
Domain
Domains are sets of :term:`DomainParticipant` that can interact with one another.
To interact they must share the same domain identifier and must have compatible :term:`discovery` and :term:`transport`.
``DomainParticipant``
``DomainParticipant`` is an :term:`Entity` that is used to create and manage :term:`Publishers <Publisher>` and :term:`Subscribers <Subscriber>`.
``Entity``
``Entity`` is the abstract base class for the main classes in the :term:`DDS`/:term:`DCPS` API, including :term:`DataReader` and :term:`DataWriter`.
All entities have :term:`QoS` and can accept :term:`Listener`\s and :term:`Condition`\s.
Instance
In the specific context of :term:`DDS` and :term:`sample`\s, instances refer to a set of samples that share a common key value.
Many parts of the DDS API involve instances, including the :term:`dispose` and :term:`unregister` operations.
See :ref:`getting_started--keys` for more information.
Interface Definition Language
IDL
IDL, specifically :term:`OMG` IDL, is a C-like language for describing data-structures and interfaces.
In OpenDDS :term:`opendds_idl` and :term:`tao_idl` are used to generate code from IDL.
Listener
Listeners are a method of being notified of events from :term:`entities <Entity>`, such a new :term:`sample` being available from a :term:`DataReader`, via asynchronous callbacks.
See :doc:`devguide/conditions_and_listeners` for more information.
Makefile, Project, and Workspace Creator
MPC
``mwc.pl``
``mpc.pl``
A build-system that generates GNU Makefiles, Visual Studio projects, and other such files.
It serves the same role that CMake, Meson, and Automake do in other projects.
See :ref:`deps-mpc` for more information.
Object Management Group
OMG
A standards organization which publishes :ref:`DDS and the other specifications used by OpenDDS <specs>`.
See https://www.omg.org/ for more information.
``opendds_idl``
A program that generates C++ code from :term:`IDL` for use in OpenDDS.
``Publisher``
``Publisher`` is an :term:`Entity` that is used to create and manage :term:`DataWriters <DataWriter>`.
Quality of Service
QoS
QoS is a set of requested policies for how :term:`entities <Entity>` should behave.
See :doc:`devguide/quality_of_service` for more information.
Real-time Publish-Subscribe
RTPS
RTPS, sometimes also called *DDSI-RTPS*, is a specification that defines how different DDS implementations can interact with one another.
See :ref:`spec-rtps` for more information.
Sample
Samples are the messages sent from :term:`DataWriter`\s and received by :term:`DataReader`\s.
``Subscriber``
``Subscriber`` is an :term:`Entity` that is used to create and manage :term:`DataReaders <DataReader>`.
The ACE ORB
TAO
TAO is a :term:`CORBA` implementation that is maintained alongside :term:`ACE`.
OpenDDS uses it for InfoRepo discovery and :term:`tao_idl`.
See :ref:`deps-tao` for more information.
``tao_idl``
A program that is part of :term:`TAO` that generates C++ code from :term:`IDL` for use in TAO and OpenDDS.
``Topic``
A ``Topic`` is an :term:`Entity` with a name and a :term:`type <Topic type>` that the system uses to figure out which :term:`DataReader`\s get a :term:`sample` from a :term:`DataWriter`.
Topic type
A topic type, sometimes also called a *data type*, is the :term:`IDL` type of a :term:`topic` and also type of the :term:`samples <Sample>` of the :term:`DataWriter`\s and :term:`DataReader`\s that use that topic.
Transport
Transports are the configurable methods that :term:`DataWriter`\s and :term:`DataReader`\s use to communicate.
Unregister
When an :term:`instance` is unregistered by a :term:`DataWriter`, it means the writer "no longer has ‘anything to say’ about the instance", as phrased by the DDS specification.
This is similar, but separate from :term:`disposing <dispose>` an instance.
They are usually done at the same time, but this can be changed using :ref:`qos-writer-data-lifecycle` and the ``unregister_instance`` method of ``DataWriter`` to make what unregister means application-defined.
XTypes
Extensible and Dynamic Topic Types for DDS
XTypes is an :term:`OMG` specification that defines how DDS systems can have :term:`topic type`\s that can evolve over time and be used without defining IDL.
See :ref:`spec-xtypes` and :doc:`devguide/xtypes` for more information.
.. envvar:: ACE_ROOT
The path of the :term:`ACE` source tree or installation prefix being used.
.. envvar:: DDS_ROOT
The path of the OpenDDS source tree or installation prefix being used.
.. envvar:: TAO_ROOT
The path of the :term:`TAO` source tree or installation prefix being used.
.. envvar:: OPENDDS_CONFIG_DIR
Makes ``-DCPSConfigFile`` paths relative to the path in the environment variable.
See :ref:`here <OPENDDS_CONFIG_DIR>` for more information.