ch13.htm

this describes managing multivendor networks

each object. When a message is sent to an object requesting action, the object will
then execute the appropriate methods. The object encapsulates data, functions, and
logic, which is then shielded from the receiving application.</P>
<P>Object technology can also simplify maintenance and network management tasks.
For example, changes and adds can be abstracted to the point of plugging or unplugging
visual objects in a graphical interface.
<H3><A NAME="Heading4"></A><FONT COLOR="#000077">OLE</FONT></H3>
<P>Component technology's goal is to permit development, management, and other tasks
through interoperable, cross-platform, off-the-shelf components. Windows developers
have at their disposal a large collection of Visual Basic ActiveX custom controls.
Based on Microsoft's <I>OLE (object linking and embedding)</I> technology, ActiveX
has evolved from the earlier VBX and OCX models. OLE, however, carries a high learning
curve and lacks object-oriented features such as inheritance, a technique whereby
both data and functions are moved from one object into a new object.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>Network OLE</B></FONT><BR>
	Microsoft is working on a version of Network OLE to provide this same functionality.
	Network OLE will use RPCs to distribute components throughout the enterprise. Network
	OLE will be released with the next version of Windows NT. It adds a third tier to
	a client/server network, with business rules and code encapsulated into components
	and distributed across the network. This third layer is transparent to the end user,
	who will not have to know where the OLE objects are located. 
<HR>


</BLOCKQUOTE>

<P>OLE (Microsoft) is based on the <I>Common Object Model (COM),</I> an open spec
for object technology. OLE objects are interoperable, and can be created in any one
of several languages. OLE is only available on Windows platforms. Microsoft's Visual
Basic 4.0 takes some steps towards a <I>Distributed OLE</I> model, which permits
VB functions to be declared remote.</P>
<P>Under pressure to at least marginally embrace open systems and the World Wide
Web, Microsoft has come up with an OLE enhancement technology it calls <I>ActiveX.</I>
Besides Windows, ActiveX supports Macintosh and UNIX, and supports a large set of
tools and programming languages. Microsoft's goal in releasing ActiveX is to make
it easier to create interactive applications and World Wide Web pages. Already, there
are more than 1,000 reusable ActiveX controls--which means that when you are building
a Web page, you don't have to build every piece from scratch. Although it doesn't
compete directly against Sun Microsystem's enormously popular Java language, Microsoft
certainly had Java's market in mind when they created this little gem. Java programmers
can access ActiveX controls from Java applets, and ActiveX also establishes a bridge
to Java to let other programming languages use Java applets as reusable components.
Microsoft's <I>Visual J++</I> Java development tool integrates the Java language
with ActiveX.</P>
<P>NeXT Computer is planning to beat Microsoft at its own game, by offering distributed
OLE technology before Microsoft releases its own distributed OLE products. NeXT plans
to ship an extension of its current OLE object environment, called <I>Distributed
OLE for Windows.</I> With this tool, developers can create Windows applications that
send OpenStep objects across a distributed network.
<H3><A NAME="Heading5"></A><FONT COLOR="#000077">CORBA</FONT></H3>
<P><I>Common Object Request Broken Architecture (CORBA),</I> however, does support
object-oriented development. <I>OpenDoc</I> is a CORBA-based platform developed by
an industry alliance led by Apple Computer, Inc. OpenDoc is better suited to cross-platform
development and works well on UNIX, Mac, and OS/2 environments. OpenDoc does support
OLE and an OLE 2.0 object can be embedded in an OpenDoc component. Because OpenDoc
is a derivative of CORBA, it is networkable. CORBA 2.0 has a method for distributing
objects throughout the enterprise.</P>
<P>CORBA's <I>ORB (Object Request Broker)</I> architecture affords developers more
freedom than OLE in terms of programming languages and operating systems. OMG's (Object
Management Group) CORBA 2.0 is based on the ORB structure. ORBs facilitate interoperability
and establish a single platform on which objects request data and services on the
client side or provide them from the server side. TCP/IP is used by CORBA as a standard
communications protocol. Compared with the other standards for distributed objects,
CORBA is still immature and lacks some features for large-scale production.</P>
<P>Version 2.0 of the CORBA specification includes the <I>Internet Interoperability
Object Protocol (IIOP),</I> which provides for multivendor connectivity. The previous
implementation of CORBA, although it provided for portability, did not include a
specification for interoperability. The availability of IIOP will significantly increase
CORBA's potential to become widely accepted.</P>
<P>The ORB model is rapidly maturing, and several vendors are bringing ORBs to market.
Some of these products extend the CORBA specification to support mission-critical
applications, by providing fault tolerance, support for shared memory, and multithreading.
Microsoft OLE-based applications will communicate with CORBA applications through
a CORBA 2.0 ORB.</P>
<P>CORBA (Object Management Group) provides the specifications for the development
of ORBs. An ORB instantiates objects, establishes communications between objects,
and invokes methods on behalf of objects. The <I>CORBA Interface Definition Language
(IDL)</I> is used to define the object's interface, but the existing specification,
1.2, does not provide for a standard communications protocol. As a result, few ORBs
are interoperable between vendors. (The next version, 2.0, will specify such a standard.)
CORBA does not specify a mechanism for locating or securing objects.</P>
<P>ExperSoft's <I>PowerBroker 4.0</I> is an extension to the XShell 3.5. It is the
only product available that supports both the Common Object Request Broker Architecture
(CORBA) 2.0 and Microsoft's OLE. This is accomplished through the product's <I>Meta
object request broker,</I> which works as a translation layer that understands the
two object models, as well as the predominant object-oriented programming languages.
CORBA 2.0 defines mappings between object-oriented languages. ORBs are a type of
software that defines how a software object is identified and used across the network.
CORBA and OLE are integrated through the PowerBroker OLE feature, which automates
interactions between OLE automation clients and PowerBroker objects.
<H3><A NAME="Heading6"></A><FONT COLOR="#000077">OpenDoc</FONT></H3>
<P>OpenDoc developers are currently able to more easily migrate a component between
platforms, and OpenDoc is much more interoperable than OLE. OpenDoc is promoted by
Component Integration Laboratories (Sunnyvale, California), an Apple-led consortium.</P>
<P>The OpenDoc (Component Integration Laboratories) consortium comprises several
vendors, including Apple, IBM, and Novell. Similar to OLE, OpenDoc is based on IBM's
System Object Model (SOM) and presents a visualization system for compound documents.
(Members of the consortium are planning to provide OpenDoc support in their applications,
and development kits have become available.) However, OpenDoc is a latecomer into
the distributed object market.</P>
<P>OpenDoc introduces a component-based architecture suitable for cross-platform
development. It is implemented as a set of shared libraries, which include the protocols
for creating software components across a mixed environment. The standard is vendor-independent,
and has a layered architecture that offers five services: Compound Document Services,
Component Services, Object Management Services, Automation Services, and Interoperation
Services. Many of the features of OpenDoc can be accessed through API calls. OpenDoc
is based on the CORBA-compliant <I>System Object Model (SOM).</I> Developed by IBM,
SOM is a tool for creating cooperative objects, it's used in the OS/2 Workplace Shell,
and has proven itself to be a reliable and mature technology.</P>
<P>The goal of OpenDoc is to enable users to call up compound documents that might
include graphics, text, or other elements, without having to invoke all the various
applications involved in creating them. Under the OpenDoc view, vendors replace their
traditional large applications with part editors and part viewers, and therefore
represents a significant change in the way software is created and used. This differs
from the traditional, application-centered model, where users call up specific applications
to create platform-specific documents. Despite large vendors' attempts at throwing
everything imaginable into one large application, it is impossible to provide every
feature that every user could possibly want. OpenDoc instead makes features separately
available as parts, so end users can customize their application environments to
suit them. Companies are starting to deliver OpenDoc parts to the market.
<H3><A NAME="Heading7"></A><FONT COLOR="#000077">DCE</FONT></H3>
<P><I>Distributed Computing Environment (DCE)</I> is one of the most mature standards.
Microsoft's OLE, because it is proprietary, is not a true standard, but has become
a de facto standard for Microsoft environments. OLE is widely used, but specifications
have not been provided to other vendors. OpenDoc is not widely accepted.</P>
<P>A product of the Open Software Foundation (OSF), DCE is fully vendor-independent
and is widely available from several vendors and most operating systems. It includes
services for locating distributed objects, and secure access facilities. It also
includes a protocol for communicating in a heterogeneous environment.</P>
<P>The widespread availability of DCE objects makes it a good framework for building
applications. The DCE <I>Remote Procedure Call (RPC)</I> is not dependent on one
protocol or network type. The DCE RPC lets a server communicate with multiple clients
on different types of networks, and DCE's <I>Global Directory Service (GDS)</I> and
<I>Cell Directory Service (CDS)</I> is a useful technique for managing an internetwork.
In this model, a local node set is represented as a CDS on the bigger GDS hierarchy.</P>
<P>DCE has been commercially available only for a short time, and supporting commercial
software products are still not widely available or are in their early stages of
development. When better tools become available, managing the distributed environment
will be easier.</P>
<P>OSF's <I>Distributed Management Environment (DME)</I> is DCE-enabled management
services. DCE's administration is consolidated under DME, providing a programmable
process for managing the distributed environment. Implementing a successful DCE migration
might take years and it requires detailed planning and strategies. Migration is hindered
by DCE incompatibilities, a slow emergence of standardization, and resistance by
users and management. While major vendors have announced DCE support, there are not
yet any application development or management tools; although some products do offer
DCE support. DCE decreases the complexity of a migration to a distributed computing
environment by reducing the amount of variables, simplifying transition, and lessening
dependence on multiple vendors.</P>
<P>The Motif GUI was one of the earliest successes of OSF. Motif has been accepted
as a standard open systems interface by most major UNIX vendors. DCE includes RPC
technology, which provides application and file sharing, enterprise security, and
directory services. These are all transparent to operating systems, hardware, and
protocols.</P>
<P>More widespread availability has led to an increase in DCE's popularity: DCE is
now available on Windows NT, MVS, and AIX. DCE is a set of integrated directory,
security, and transport services for building distributed applications that can run
over multiple operating systems. It can support large-scale distributed environments
in a multivendor environment. Other object technologies lack the same level of standardization
and security to be effective in an enterprise-wide multivendor environment. More
tool vendors are bringing products to the market that make DCE programming easier.