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Architecture |
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Analysis
of Borland/Visigenic VisiBroker
family
by Maria Gina Sian
Introduction
Founded in 1983, Borland is
one of the leading providers of software
products for corporate application developers.
It provides a family of rapid application
development tools and scalable middleware
technology. In the past, Borland has focused
primarily on the goal of "making
development easier".
In 1997, Borland expanded
this goal to include distributed object
computing. To help reach this goal, it
acquired Visigenic in 1998, which is a leading
supplier of object middleware based on the CORBA
standard."The joint vision will
target a solution that not only sets the
standard for high-performance, but will also
make it as easy to create distributed,
multi-tier applications as it is to create
two-tier client/server applications today"
[Inprise Corporate White
Paper].By supporting CORBA, the
VisiBroker product family is one of the tools
that support this vision.
Comparison
Points
Product Family
The
VisiBroker family of products consists of the
following:
- VisiBroker for Java ORB and
VisiBroker for C++ ORB - CORBA ORB for both Java and
C++ environments
- VisiBroker Integrated Transaction Service
(ITS) - Transaction solution for distributed
object applications
- VisiBroker SSL Pack and VisiBroker
Gatekeeper - Provides authentication, encryption, and
network security to distributed
applications
- VisiBroker Naming Service - Implementation
of the CORBA Naming Service
- VisiBroker Event Service - Implementation
of the CORBA Event Service
- VisiBroker Manager - Provides visual access to
ORB information and
configuration
Compliance to
CORBA
The VisiBroker for
Java ORB and for C++ ORB are fully compliant
with CORBA ORB version 2.1 specification.
According to Visigenics, VisiBroker is the first
CORBA 2.0 ORB completely written in
Java.
Architecture
VisiBroker has a native
implementation of OMG's Internet-Inter-ORB
Protocol (IIOP). This ensures the
interoperability of VisiBroker objects with
other ORB objects.
VisiBroker
supports single-threading and
multi-threading. It provides two thread
models for multithreaded servers: thread-per-session and
thread pooling.
Under the thread-per-session architecture, each
new client that connects results in a new worker
thread being created to serve that client.
When the client disconnects, its designated
worker thread is destroyed. Under the thread pooling
architecture, one worker thread is assigned
to a client request but only for the duration of
that request, and not for the lifetime of the
client connection. After the request is
completed, the thread is placed in a pool of
available of threads and is free to service
other client requests. This architecture
reduces the overhead from creating and
destroying threads since threads are constantly
being reused. [VisiBroker for C++ Programmer's
Guide, Chapter 8 "Managing Threads
and Connections"].
Targeted
Programming Languages and
Platforms
The
VisiBroker ORB is available for the C++ and Java
environments. Through the IIOP
implementation, objects in either ORB can
communicate to each other, as well as to other
ORB vendor objects. VisiBroker is
available in many platforms including Sun
Solaris HP-UX, IBM AIX, SGI IRIX, Digital UNIX,
and Windows 95/NT.
Development, Administration, and
Deployment
The development
process for a VisiBroker application is similar
to most CORBA ORBs. First, you write your
specifications using IDL. Then, you use
the VisiBroker's IDL compiler to generate the
client stub code and the server skeleteon
code. For the VisiBroker for C++ ORB, you
use the idl2cpp
command. For the VisiBroker for Java ORB,
you use the idl2java command. After running
the IDL compiler, you then write the client
code, which includes initializing the ORB,
binding to the appropriate objects, and invoking
the necessary methods. At the same time,
you can also write the server code, which
includes implemented the required methods and
the server's main
routine. Once the client code has been
completed, you then compile and link it with the
client stub. Similarly, you compile and
link the server code with the server skeleton
once the server code has been completed.
Before you can run the client and the server,
you also need to start the Smart Agent.
Once that it started, you can start the server
and run the client program. The VisiBroker ORB
must be installed on every client and server
machine.
VisiBroker provides the following set of
tools for administering the ORB during the
development phase.
- VisiBroker Manager -
provides a graphical tool for managing
distributed objects [This is a separate product
and is not included with the ORB.]
- irep - manages the
Interface Repository
- oad -
manages the Object Activation Daemon
(OAD)
- oadutil list
- lists ORB object implementation registered
with the OAD
- oadutil reg -
registers an ORB object implementation with the
OAD
- oadutil
unreg - unregisters an ORB object
implementation with the OAD
- osagent -
manages the Smart Agent
- osfind
- reports on objects running on a
given network
- idl2ir -
allows you to populate an interface repository
with interfaces defined in an IDL file
- idl2cpp -
generates C++ stubs and skeletons from an IDL
file
- idl2java -
generates Java stubs and skeletons from an IDL
file
For
detailed information about these tools, see Chapter 6 "Using
Administration tools" in VisiBroker for C++ Installation and Administration Guide
and Chapter 3, "Programming
tools" in the VisiBroker for C++
Reference.
Accessing CORBA
Objects
In order for the
client program to communicate with the server
object, it needs to first obtain a reference to
that object. In VisiBroker, there are 3
ways to obtain an object reference. One is
by invoking the bind method. This method is
automatically included in your object by the IDL
compiler. When the bind
method is called, the ORB contacts the
Smart Agent to locate an object implementation
that offers the requested interface. When
an object implementation is found, the ORB
connects the client program to the object
implementation. If the object
implementation is on a separate process as the
client program, the ORB creates a proxy object
upon connection, which the client uses to invoke
methods on. "VisiBroker automatically
determines the most efficient way to establish a
connection between a client program and an
object implementation" [VisiBroker for C++
Programmer's Guide, Chapter 5
"Accessing distributed objects with object
references"].
Another way of obtaining an
object reference is by stringification. VisiBroker
provides an object_to_string() method that
converts an object reference to a string.
To convert the string to an actual object
reference, the string_to_object() method can be
used.
A third way of obtaining an
object reference is through the VisiBroker
Naming Service (see Implemented CORBA Services
section below).
COM/CORBA
Integration
"Visigenics
supports software bridges to enable
communications between DCOM and CORBA
objects. VisiBridge allows ActiveX
controls implemented in Web pages, Visual Basic
applications, or OLE-enabled applications to
interoperate with CORBA objects.
Developers using ActiveX-enabled development
environments can transparently access CORBA
objects over the Internet or corporate intranet
without having to know CORBA" [Inprise Corporate White
Paper]
Implemented CORBA Services
VisiBroker provides
implementation of the following
services:
- Naming
Service. This service allows you to associate one
or more logical names with an object
implementation and store those names in a
namespace. As mentioned above, the Naming
Service is also one of the ways that a client
program can obtain an object reference.
For the main differences between locating an
object implementation using the Naming Service
and using the Smart Agent, see the Naming and Event Services
Programmer's
Guide.
- Event
Service. This service "provides a
facility that de-couples the communication
between objects. It provides a
supplier-consumer communications model that
allows multiple supplier objects to send data
asynchronously to multiple consumer objects
through an event channel" [Installation and Administration
Guide, Chapter 2 "VisiBroker
Basics"].
- Transaction. The VisiBroker Integrated Transaction
Service "simplifies the complexity of
transaction management by integrating an
essential set of services into one
product--including transactions, integration
with databases and legacy systems, and
administration tools for managing enterprise
applications." One of these services
is the Transaction Service. This component is a
compliant implementation of the CORBA
Transaction Service, version 1.1, that manages
the completion of the transaction. It works with
objects at the ORB level to coordinate and
manage a transaction's commit or rollback. It
also interacts with an application when a
transaction begins or coordinates the
transaction's commit or abort across multiple
objects" [ITS Administrator's Guide,
Chapter 2 "VisiBroker ITS
Basics"].
- Security. "VisiBroker's optional
SSL feature uses the industry-standard Secure
Sockets Layer Version 3 (SSL) protocol,
developed by Netscape Communications
Corporation, to establish secure connections
between clients and servers" [VisiBroker for C++ SSL Pack Programmer's
Guide, Chaper 2 "Getting Started
with SSL"]. It provides
important security features such as
authentication, privacy, and
integrity.
- Persistence.
"VisiBroker allows you to implement
objects that persist beyond the life of the
implementation server by saving the objects to a
text file, database, or object database. When an
object implementation is activated, the object
is initialized from the storage device and when
the object is deactivated, its state is saved to
the storage device" [VisiBroker for C++ Programmer's
Guide, Chapter 18 "Enabling object
persistence using the Object Database
Activator"].
Partnerships and
Awards
Inprise
has partnerships with companies such as
Netscape, Cisco, Oracle, and Novell.
Inprise claims that through such partnerships,
"VisiBroker has become the de facto CORBA
solution" [VisiBroker 3.2 for Java and
C++ Solution
Sheet].
VisiBroker won DBMS
Magazine's 1997 Readers' Choice Award for Best
Object Request Broker [Borland to Acquire
Visigenic Press Release,
11/18/97]. A study by the Object
Consulting Inc., which compared IONA's OTM and
Inprise's ITS technology based on factors such
as performance, scalability, and throughput,
concluded that ITS outperforms the OTM in
several factors [Object Consulting Inc.
CORBA/OTS Performance].
Pricing
VisiBroker 3.0 for Java costs $1995 per
developer on Windows and $2995 per developer on
Unix. This does not include the Naming and
Event services.
Related
References
ORB
Comparison
Introduction
IONA Orbix
family
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