| DCOM Explained by Rosemary Rock-Evans Digital Press ISBN: 1555582168 Pub Date: 09/01/98

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Their Web site for more details about the Software AG ports, particularly the timescales for the ports, can be found on http://www.sagus.com. This Web site also contains downloadable versions of DCOM for the ports available in beta.

Hewlett Packard-is intending to port DCOM to HP-UX. The announcement was made in May 1997, when Hewlett Packard announced their intent to provide COM technology, including DCOM features, on HP-UX “within the year.” A summary of the planned platform support is shown below in the table.

One important aspect worthy of special mention is that the other ports of DCOM on the platforms shown generally work only with Windows NT, not Windows95. This means that the developer needs a three-tier architecture to use DCOM, with Windows NT or 95 clients accessing a Windows NT server which can then, in turn, communicate with other platforms. In fact, this is the sort of architecture Microsoft is encouraging, with other platforms acting more as servers and the Windows NT platform acting as a sort of hub.

Table 11. 1 Platform support
Operating system | DCOM | Who
--- | --- | ---
UNIX | AIX | Planned | Software AG
| HP-UX | Planned | HP, Software AG
| Solaris | YES | Software AG
| SINIX | Planned | Software AG
| Linux | YES | Software AG
| SCO UnixWare | Planned | Software AG
| Digital Unix | Planned | Digital, Software AG
| IRIX | YES | Silicon Graphics
PC | Windows95 | YES | Microsoft
| Windows NT WS | YES | Microsoft
| Windows NT Svr | YES | Microsoft
| Macintosh | YES | Microsoft
Propty | Open MVS | YES | Software AG
| OS/400 | Planned | Software AG
| OpenVMS | Planned | Digital, Software AG

Figure 11.2 Windows NT acts as a hub in three-tier architecture

Furthermore, the network protocol supported is TCP/IP to all platforms except MVS when Cedar is being used.

### What Is Provided?

DCOM on other platforms is provided as a runtime environment and a Software Development Kit (SDK).

The runtime environment comes as a set of shared runtime libraries (DLLs or equivalent) used for supporting the applications at runtime together with a set of administration tools, such as a utility to enable servers (proxy and stub libraries) to be registered, and installation utilities. Be aware that the runtime takes up over 20MB of disk space.

The SDK consists of a set of tools, libraries, and examples which typically include:

  • An MIDL compiler-which can be used to generate stubs and proxies. Sample files are often provided with the ports
  • An ActiveX Template Library-a Unix implementation of the Microsoft ATL
  • GUIDgen (the tool to generate GUIDs)
  • UUIDgen-this looks up the registry to get the address of the network interface card in the way we described in the chapter on GUIDs
  • header files-a set of header files for inclusion in source files for compilation
  • make files-the makefile utility is provided as a Bourne shell script in Software AG’s Unix port, for example. The utility generates a C++ module that has to be compiled and linked with the shared libraries.
  • mktyplib-the make type library utility

These are generally command line driven at the moment rather than being GUI-based tools. Clearly the actual tools provided depend on who is providing the port, but the principle is much the same.

We will be saying a little more about wrapping in this chapter, but Digital is also aiming to provide wrapping technology via third-party companies.

### Concepts Supported

The table below shows the COM concepts which can be supported and how they are supported. This table thus shows what limitations there are from the developer’s point of view when building an application. In the next section we will show the functions available.

Table 11.2 Concept support
Concept | Supported?
--- | ---
Component | YES
Interface | YES
Moniker | YES (registering, stringification, binding file, and composite, etc.)
Automation | YES (IDispatch and the type library)
Aggregation | YES
MIDL | YES

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