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9.3) ITASCA (Commercial Systems - OO Data Model - Object-oriented Databases And Vendors)




Description

This article is from the Object-Oriented Technology FAQ, by Bob Hathaway rjh@geodesic.com with numerous contributions by others.

9.3) ITASCA (Commercial Systems - OO Data Model - Object-oriented Databases And Vendors)

Introduction

Itasca Systems develops, markets, and supports ITASCA, a distributed
active object database management system and related tools. The initial
research work for ITASCA occurred in the Object-Oriented and Distributed
Systems Lab at the Microelectronics and Computer Technology
Corporation (MCC) in Austin, Texas. The research was known as the
ORION prototypes.

The ITASCA Distributed ODBMS is a language neutral, full-featured, active
object database that supports data access from various object
languages. ITASCA allows clients to transparently access data that is
distributed among multiple servers. ITASCA supports full dynamic schema
modification that can be performed during any phase of the software
lifecycle. Applications written in dissimilar and incompatible languages,
such as C++ and CLOS, share objects through ITASCA. ITASCA stores methods
inside the database, promoting reusability and maintainability. The only
commercial ODBMS based upon the MCC Orion technology, ITASCA is considered
by many to be the most feature-rich ODBMS on the market today.

This overview describes release 2.2 of the ITASCA Distributed Object
Database Management System. It describes how ITASCA functions,
outlines its implementation features, and explains some of the system
benefits.

History of ITASCA

ITASCA is based on a series of object database research prototypes. Work
on these prototypes began in 1985 at the Microelectronics and Computer
Technology Corporation (MCC) Object-Oriented and Distributed Systems
Laboratory. MCC released the first prototype, ORION-1, in May, 1987, as
a single-user system. MCC extended ORION-1 to the ORION-1SX
prototype system and released it to the shareholder companies in April,
1988. ORION-1SX was a multi-user system with a multi-client, single
server architecture. The third prototype, ORION-2, introduced a distributed,
object-oriented architecture for a multi-user environment. MCC released
the third prototype to shareholder companies in July, 1989. ORION-2 has a
multi-client, multi-server architecture. Having met its objectives, MCC
stopped all work on ORION at that time. Over five million dollars was spent
for the three generations of prototypes.

The ITASCA product is an extension and commercialization of the ORION-2
prototype from MCC. Itasca Systems has added major enhancements and
features, improved the performance, and strengthened the code. It now runs
on UNIX systems from multiple vendors. ITASCA is an industrial-strength,
documented product, fully supported by Itasca Systems, Inc. Itasca Systems
continues to develop tools and other products to work with ITASCA.

Overview

ITASCA employs a distributed architecture with private and shared objects
spread across UNIX-based computers on a local-area network. The
ITASCA model follows the object-oriented view that uniformly models any
real-world entity as an object. Each object has a unique identifier along with
a state and behavior. Attributes represent the state of an object. Methods
(code) define the behavior of an object. A class object collects objects that
share the same set of attributes and methods. Subclasses derive from
existing classes. The resulting schema, or database definition, is a class
hierarchy. Each subclass inherits all the attributes and methods of its
superclasses. ITASCA supports multiple inheritance. A subclass may derive
from more than one superclass.

One of the breakthroughs of object-oriented technology is the reusability of
code. ITASCA allows for the active management of both reusable code and
data in an integrated system. Developers may write applications in C++,
CLOS, C or Common Lisp. This means ITASCA is language neutral. Objects
stored using one programming language can be accessed by other
programming languages. It also means an application program need not be
written in an object-oriented language.

The ITASCA database management system has features belonging to most any
database system. This includes persistent storage for data and schema,
concurrency control and locking, transaction management, multiple
security levels, and logging and recovery for both CPU and disk media
failure. Additional features of ITASCA include dynamic schema
modification, long-duration transactions, shared and private databases,
distributed version control, distributed transaction management, distributed
query management, distributed change notification, object migration, and
an extensible architecture.

Shared and private databases exist in a distributed environment in ITASCA.
The shared database is distributed across workstations (sites) in a network.
An ITASCA server controls the partition of the shared database at each site.
ITASCA clients provide transparent access to the various partitions of the
shared database. The architecture allows any number of private databases at
each distributed database site. Data can move between private and shared
databases. Private databases allow private data that is not shared with other
users of the database.

ITASCA stores the schema redundantly at each site to improve
performance. The schema storage also includes code in the form of
methods. Management of schema updates is automatic for all sites. This
includes sites that were off-line during any changes. Automatic distribution
of schema changes, including method code changes, simplifies database
administration.

ITASCA stores each instance of data in one site. The system or a user may
move the data from one site to another to improve data locality. Access to
moved data remains transparent. There is no need for a user or application
to know the specificlocation of data in the ITASCA distributed database.
ITASCA will automatically find the location of the data. This simplifies
distributed application development. The developer can rely on ITASCA
finding data in the distributed database.

No single site acts as a master site, thus ITASCA's architecture has no
single point of failure. ITASCA has neither a central data server nor a
central name server. This is important for maintaining a database system
with high availability in a networked workstation environment.

ITASCA supports dynamic schema modification to create a flexible
environment for changing or customizing a database system. Authorized
users can add and remove attributes or change the subclass/superclass
relationship at any time. Authorized users can also add or remove partitions
of the shared database at any time. All this can be done interactively without
affecting other parts of the ITASCA database at the time changes occur to
the schema. There is no need to "bring the system down" or off-load/reload
data to restructure the database. Dynamic schema modification can
significantly reduce maintenance costs. It also is useful in environments
where change to data definitions are normal or relatively frequent.

ITASCA has a sophisticated security authorization technique tied to the
class hierarchy. It supports both positive and negative authorizations at any
level in the class hierarchy. For example, granting access to all objects but
one requires only two authorizations: a global grant followed by a specific
denial. Authorization extends to classes, instances of classes, attributes,
and methods. Also, inheritance of authorization reduces the work of database
administration.

Long-duration transactions allow users to check objects out of the shared,
distributed database into their private databases. Users can then change the
objects in the private databases without affecting the shared database or
other users. These changes can be committed to the private database. Then,
at any later time, the user can check the updated object or objects back into
the shared database.

ITASCA supports version control of objects. A new version of an object
promotes the original or parent object to restrict further changes to the
parent. ITASCA also supports alternate versions such that multiple versions
can have the same parent. Promoting an object version to a released status
restricts any deletion of the object. ITASCA uses generic versions to
dynamically reference the most recent or default version of an object
without any intervention by a user or application.

Change notification in ITASCA is either flag-based or message-based.
Flag-based notification will identify an updated object upon querying the
object for such information. It is a passive notification scheme. Message-
based notification, on the other hand, is an active notification scheme. It
will execute a method (or code) upon an update or other change to an object.
Such methods can send mail messages or invoke other methods or
programs.

Memory management in ITASCA uses both page and object buffers.
ITASCA has a traditional database page buffer scheme that contains pages
with multiple objects. Desired objects move from the page buffer to an
object buffer. The object buffer then provides ITASCA with enhanced in-
memory performance because it contains only frequently-referenced
objects.

IBEX Corporation

ITASCA is a distributed active object database management system and
related tools. The ITASCA Distributed ODBMS is a language neutral,
full-featured, active object database that supports data access from
various object languages. ITASCA allows clients to transparently access
data that is distributed among multiple servers. ITASCA supports full
dynamic schema modification that can be performed during any phase of the
software

A point release of ITASCA (2.3.5) was delivered to customers with current
service contracts in September 1995. Development continues with the
expectation of ODMG compliance in the next full release, scheduled for
1996.

IBEX has built its DAWN Distributed Archiving and Workflow Network class
library of methods and development tools as an application framework to
speed the development of customized solutions to enterprise-level
integration problems. ITASCA's installed based has been largely in
manufacturing and engineering until now, but with DAWN, banking and other
services are beginning to take advantage of the products extended
functionality. DAWN is also used to link production and front office
environments for active decision support. The DAWN Manager Series comprises
focused applications (developed on ITASCA with DAWN), such as DAWN 9000 and
DAWN Account Manager which have an embedded Optical Character Recognition
functionality linked to the database with a customer-defined workflow.

IBEX has re-activated the ITASCA ObjectShare Library and encourages clients
to contribute reusable objects for use by registered ITASCA customers.
Several HTML and Web Browsers for the server itself are underway.

ITASCA was very well rated in a 1994 BUtlerBloor comparison of Object
Databases (the only one to receive more than one uncontested first rating
-- it got four!

Three framework papers describing IDE and CALS in more detail may be found
at Web site http://www.acq.osd.mil/cals/

IBEX Computing
International Business Park
4e Bd., Bat. Hera
74160 Archamps
France

Email: ibex@iprolink.ch
Voice: +33 50 31-5700
Fax: +33 50 31-5701

Web: http://www.iprolink.ch/ibexcom/

IBEX Object Systems, Inc. (North American office)
Minneapolis, MN 55401
U.S.A.

Voice: (612) 341-0748
Fax: (612) 338-5436

 

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