The models and their evolution COM DCOM come to be the major steps to define the standard architecture of industrial communications and computer interfaces, based on and because they think the communication standard OPC (OLE for Process Control) used today plants in all the world to communicate data from plant to the various control system applications installed.
End this section, talking a little more of these models then in the following items demos go to great OPC.
Component Object Model: COM
COM is a model for binary code developed by Microsoft, allows programmers to develop objects that can be accessed by any application that meets the standard. Objects can sje iteractuar with others who are in the same application as another application. Provides services for the interfaces of objects, lifetime management (when an object can be removed from the system), and other events.
All implementations of COM are the client - server architecture. All objects are accessed via COM interfaces, customers see only the interfaces. OLE and ActiveX are based on COM.
COM Architecture Example
Consider a system service API (application program interface) that lets you use a service provider transparently. The service manager allows consumers to connect to the provider, however once connected the service manager is still the way of communication, so it is overloaded. Service levels are limited by the service manager, the provider is limited to levels that can have the Service Manager version used.
Figure 3.3 Traditional System Service
In object-oriented programming, no matter what each provider is required a structure to connect, that structure is set by COM. The software components are pieces of software in binary form easy to reuse. COM allows applications to communicate as software objects.
Figure 3.4 Binding through COM
A difference with a traditional API is that when communication is established COM disappears from the scene, the client and object communicate directly.
The development and evolution of objects is permitted, the objects can add new interfaces to communicate with new customers.
Distributed COM: DCOM
The objects of the client programs can access the objects of the server programs located on other computers on the network. It uses TCP / IP HTTP. It is part of Windows since NT 4.0 and versions can be installed from Windows 95.
Allows another level of functionality of OPC, so that customers can use objects on other computers on the network. A software package HMI SCADA or can exchange data in real time with servers running on any computer on the network. The OPC has a mechanism to browse OPC servers and access their content items. Manufacturers use this specification for servers and clients to create real-time information exchange between systems such as DCS, SCADA, PLCs, distributed systems, Input / Output, intelligent field devices and industrial networks.
Figure 3.5 Link via DCOM
