OMG DDS Specification V1.2：实时系统数据分发服务详细规范

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OMG DDS Specification V1.2 是一份由Object Management Group (OMG)发布的官方规格文档，针对实时系统的数据分布服务(Data Distribution Service, DDS)进行详细规定。该文档于2007年1月发布，版本号为1.2，包含了多个公司的版权声明，如Objective Interface Systems, Inc., Real-Time Innovations, Inc., 和 Thales等，它们共同授权OMG在非独家、免版税且一次性付费的基础上在全球范围内复制、分发此规格，并允许对其进行修改后再次分发。作为一份正式的标准，该规格文档明确了其使用条款、条件和注意事项。它并非承诺任何公司会将其纳入产品实现，而是文档内容可能会根据需要进行无通知的变更。这份文档的重要性在于它为实时系统的数据交换提供了一套统一的规范，定义了如何高效、可靠地在分布式环境中进行实时数据传输，这对于嵌入式系统、自动驾驶、航空航天等领域至关重要。其中，可能包含的主题包括： 1. **DDS架构** - 描述了DDS的基本组件（如Publisher、Subscriber、Topic、Message等），以及它们在实时通信中的作用。 2. **服务质量(QoS)** - 规定了数据传输的可靠性、延迟、带宽和流量控制等方面的要求，确保在严苛的实时性应用中数据的一致性和完整性。 3. **数据模型与类型支持** - 如何定义和使用不同的数据类型，以及如何通过Topic来组织和传递这些数据。 4. **发现与连接** - 描述了节点之间的自动发现机制，使得参与者能够找到并连接到正确的数据源或订阅者。 5. **多平台兼容性** - 提供跨操作系统和硬件平台的标准化接口，使得不同厂商的产品可以无缝集成。 6. **安全性与隐私** - 可能涉及数据加密、访问控制和身份验证机制，以保护敏感信息。 7. **性能优化** - 对于大规模并发和高吞吐量场景的处理策略，包括消息缓存和负载均衡等。 8. **API与SDK** - 提供了编程接口和开发工具，帮助开发者快速理解和实现DDS功能。 OMG DDS Specification V1.2 是一个关键的技术文档，为实时系统的开发者和实施者提供了必要的指导，对于构建高性能、可靠的分布式数据基础设施具有重要的参考价值。

4 Data Distribution Service for Real-time Systems, v1.2

•

Real-Time Innovations, Inc.

• THALES

• The Mitre Corporation

• University of Toronto

Data Distribution Service for Real-time Systems, v1.2 5

7 Data-Centric Publish-Subscribe (DCPS)

This chapter describes the mandatory DCPS layer. The DCPS layer provides the functionality required for an application

to publish and subscribe to the values of data objects.

It allows:

• Publishing applications to identify the data objects they intend to publish, and then provide values for these objects.

• Subscribing applications to identify which data objects they are interested in, and then access their data values.

• Applications to define topics, to attach type information to the topics, to create publisher and subscriber entities, to

attach QoS policies to all these entities and, in summary, to make all these entities operate.

The description is organized into two subsections:

• The Platform Independent Model (PIM).

• The Platform Specific Model (PSM) for the OMG IDL platform based on the PIM.

7.1 Platform Independent Model (PIM)

7.1.1 Overview and Design Rationale

7.1.1.1 Format and conventions

The purpose of this subsection is to provide an operational overview of the DCPS PIM. To do so, it introduces many

terms. Some of them are common terms whose meaning, in the context of publish-subscribe, is different from common

usage. In cases where it is deemed appropriate, such terms will be italicized. Other terms are unique to publish-subscribe

and/or to this specification, and are incorporated as key elements of the Class Model. The first time such terms are used,

they will be formatted with Bold-italics

. Subsequent occurrences may not be highlighted in any way.

In addition to the UML diagrams, all the classes that constitute the Service are documented using tables. The format used

to document these classes is shown below:

1. In this case, the written name is exactly the one of the corresponding class, which forbids the use of the plural. In case this would

lead to ambiguity, it has been followed by 'objects' to state that there may not be only one of these.

attributes

...

operations

8 Data Distribution Service for Real-time Systems, v1.2

7.1.1.2 Conceptual Outline

7.1.1.2.1 Overview

Figure 7.1 - Overview

Information flows with the aid of the following constructs

: Publisher and DataWriter on the sending side, Subscriber

and DataReader on the receiving side.

• A Publisher is an object responsible for data distribution. It may publish data of different data types. A DataWriter

acts as a typed

accessor to a publisher. The DataWriter is the object the application must use to communicate to a

publisher the existence and value of data-objects of a given type. When data-object values have been communicated to

the publisher through the appropriate data-writer, it is the publisher’s responsibility to perform the distribution (the

publisher will do this according to its own QoS, or the QoS attached to the corresponding data-writer). A publication is

defined by the association of a data-writer to a publisher. This association expresses the intent of the application to

publish the data described by the data-writer in the context provided by the publisher.

• A Subscriber is an object responsible for receiving published data and making it available (according to the

Subscriber’s QoS) to the receiving application. It may receive and dispatch data of different specified types. To access

the received data, the application must use a typed DataReader attached to the subscriber. Thus, a subscription is

defined by the association of a data-reader with a subscriber. This association expresses the intent of the application to

subscribe to the data described by the data-reader in the context provided by the subscriber.

Topic objects conceptually fit between publications and subscriptions. Publications must be known in such a way that

subscriptions can refer to them unambiguously. A Topic is meant to fulfill that purpose: it associates a name (unique in

the domain

), a data-type, and QoS related to the data itself. In addition to the topic QoS, the QoS of the DataWriter

3. All those constructs are local to the application part. Actually they play the role of proxies to the service.

4. 'typed' means that each DataWriter object is dedicated to one application data-type.

5. Broadly speaking, a domain represents the set of applications that are communicating with each other. This concept is defined more

precisely in Section 7.1.1.2.2, “Overall Conceptual Model and Section 7.1.2.2.1, “DomainParticipant Class,” on page 22.

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