Object-Orientation FAQ

Introduction:

Objectivity/DB has a fully distributed client/server architecture that
transparently manages objects distributed across heterogeneous environments and
multiple databases.  It provides an application interface that uses transparent
indirection to ensure integrity and provides a single logical view of all
information, with all operations working transparently on any database on the
network, with scalable performance as users and objects increase.  A
higher-level Object Definition Language (ODL) is available as well as a C
functional interface, integrated C++ interface, and SQL++.

Objectivity/DB

Objectivity/DB [Reference:  Technical Overview, Objectivity, 1993], a product
of Objectivity, Inc. of Menlo Park, CA, provides an integrated C++ programming
interface with an emphasis on the DBMS engine for robustness and scalability
from workgroups to enterprise-wide production applications.  In production use
today with more than 50,000 end users licensed, it supports a fully
distributed, rather than central-server, architecture, with all operations
working transparently over a mixture of multiple databases, schemas, users, and
computers, and over heterogeneous hardware, operating systems, and networks.
The language interface includes a C++ class library interface, soon to be ODMG;
a C function library; and SQL++, supporting query predicates with either SQL or
C++ syntax, interactively or programmatically.  Over forty administrative and
GUI tools provide both an interactive and programmatic interface, and a
messaging backplane allows third party tools integration at four different
levels, with a list of partners at all levels.

One of the key architectural concepts of Objectivity/DB is an object reference
mechanism that ensures data integrity.  Unlike traditional ODBMSs that use
direct pointers, which become invalid after commit and hence lead to crashes
and corrupt databases, Objectivity/DB uses an indirection to guarantee safe
reference.  Transparent to the user, this indirection requires an extra test
and pointer dereference, or a couple of cycles, which is not measurable in most
applications.  However, it ensures integrity of all references, even across
transaction boundaries, resulting in production quality robustness.  Also, it
provides object level granularity for the object manager, allowing it to move,
cluster, and swap objects as necessary, one of the keys required for
scalability in objects and users.  Finally, it allows object-level granularity
for current features, such as heterogeneity and versioning, and future
extensions, such as object-level security.

A higher-level Object Definition Language (ODL) is provided that allows
declaration of modeling concepts such as bi-directional associations, behavior
of associations between objects as they version (move, copy drop), and
propagation of methods across associations.  These then result in automatically
generated methods and declarations for both C++ and C.  The standard C++ API
allows application programmers to work with any standard compilers and
debuggers, with no extra pre-processors, providing ODBMS capabilities via
overloading C++ operators (new, ->, etc.), and declarations via provided
classes (for references, etc.).

Workgroup through enterprise-wide and cross-enterprise computing is supported
via a distributed client/server architecture that provides a single logical
view over multiple databases on heterogeneous machines.  The user sees a
logical view of objects connected to objects and need not worry that one object
is in a database on a Sun workstation, while another may be in a database under
Windows or VMS.  All operations work transparently across this environment,
including atomic transactions with two-phase commit, propagating methods, and
versioning.  Objects may be moved between databases and platforms without
affecting working applications or requiring changes to the applications.
Multiple schemas may be created, without affecting other users or databases,
and may be used simultaneously with shared schemas, allowing local groups to
define their own models but still connect to other groups.  Databases may be
detached from this shared environment (federated database) and used on portable
devices, reconnected or moved to different (compatible) environment, or
distributed as parts or image libraries.  Gateways to RDBMSs are provided via
third-party integration with Persistence Software, and more generally to any
foreign data store, as long as the user installs the appropriate access
methods, extending the single-logical-view to include read/write access to
arbitrary foreign data stores.  Together, these allow delegation of
responsibilities to the appropriate users, integration with existing systems,
and gradual migration toward full enterprise-wide sharing.

The on-demand object manager directly and automatically manages object access
and buffering, rather than relying on system facilities such as virtual memory
or user manual get/put calls.  Mechanisms used include multiple buffer pools
locally and remotely, b-trees, hashing, scoped names, keys, and iterators, with
distributed catalogues for schemas and databases.  A direct connection is
established between the user and the objects used, so that users do not
conflict unless and until they are competing for the same objects, thus
avoiding the traditional central-server bottleneck.  Short transactions are
based on traditional (transient) locks, owned by the process, and group
together an arbitrary set of operations.  Long transactions are based on
persistent locks, owned by the user, and provide the same arbitrary grouping.
Default concurrency is two-phase locking and serialization, but extensions
available include MROW, or multiple-readers concurrent with one-writer, and
allow users to lock with or without wait or with timed waits, to implement more
sophisticated mechanisms.

Objects may be modeled using C++ structures augmented by classes provided such
as strings, dictionaries, and relationship management, as well as some
particular domain libraries.  A simple object is a C++ class (or C structure)
with associated access methods.  A complex object may include multiple varrays,
each being a dynamically varying sized array of arbitrary structure.  A
composite object is any network of related objects that acts as a single
object, both structurally and behaviorally, via propagation of behaviors to
component objects.  Any number of composite objects may be contained in
composite objects, and a single object may participate in any number of
composites.  The relationship mechanism supports uni- and bi-directional
relationships, one-to-one, one-to-many, and many-to-many.  Versioning is
supported at object granularity, may be turned on or off at any time for each
object, may be restricted to linear or allow branching with multiple writers.
References to versioned objects may be to a specific version or to the default
version, which may be separately specified by a method and may allow multiple
defaults.  Schema and object evolution are supported via versioning of the
type-defining objects.  Each time a type definition is changed, its defining
object is versioned, allowing arbitrary changes.  Objects may then be instances
of the old or new type version.  Object evolution or upgrading to the new type
version is supported  by the user writing conversion methods which are
installed and invoked by the system.

ANSI SQL query is supported in the SQL++ product.  Predicate syntax may be
either C++ or SQL.  The ODBC and SQL Access Group (SAG) protocols are
supported.  Queries may be invoked programatically or interactively, with ad
hoc support.  Access to object features is available via methods and traversal
of relationships.

Over forty administrative and developer tools are provided, each with both an
interactive and programmatic interface.  These include GUI object and type
browsers, query browsers, report generator, tools to examine and force short
and long locks, to move objects and databases, etc.  On-line incremental backup
provides a consistent network-wide snapshot, including referential integrity
across all databases, and runs incremental and full database backups with no
need to acquiesce the databases and no interference with active applications.
All tools are built around a messaging backplane, which supports four levels of
integration with user and third-party tools.  Integrated products include HP
SoftBench (full operational level), CenterLine's ObjectCenter (tool level),
Persistence RDBMS gateway, PTech and ProtoSoft Design and Analysis (language
level), and XVT and UIM/X (compatibility level).

Objectivity/DB is resold by Digital Equipment Corporation as DEC Object/DB,
providing a multi-billion-dollar second source vendor.  Over 50,000 end users
are licensed in production use, with applications including real-time
telecommunications, aerospace, defense, case, CAD/CAM, CIM, manufacturing, oil
& gas, process control, transportation, multi-media, case, document management,
financial analysis, and corporate information management.  Platform support
includes all Sun, all DEC (including VMS, alpha, OSF-1), HP/9000 series (both
68xxx and PA-RISC), IBM RS/6000, NCR 3300, SGI, Windows 3.1, and Windows NT.

On Schema Evolution (from original survey):
In the just-released Version 2.0 (shipping Oct 92), schema evolution
is supported via dynamic versioning of type-defining objects [ie.
class versions -- SMC], and via a step-by-step approach that allows
conversion of instance data via user-provided conversion methods.
Also, a full dynamic type manager interface is available for doing
fancier things.

Objectivity, Inc.
301B East Evelyn Avenue
Mountain View, CA  94041-1530
U.S.A.

Voice:     (415) 254-7100
Fax:       (415) 254-7171
Toll Free: 1-800-676-6259   1-800-SOS-OBJY