Object-Orientation FAQ

IDL (Persistent Data Systems)

IDL is a schema definition language. Schema modifications are defined
in IDL, requiring ad-hoc offline transformations of the database, in
general.  A simple class of transformations can be handled by
IDL->ASCII and ASCII->IDL translators (i.e., integer format changes,
list->array, attribute addition).
[conversation with Ellen Borison of Persistent Data Systems]
ADDITIONAL REFERENCES:
        John R. Nestor. "IDL: The Language and Its
        Implementation". Prentice Hall. Englewood Cliffs,
        NJ., 1989.
> Kala
                         Kala Technical Brief
Summary
Kala(tm) is a Persistent Data Server managing distributed, shared,
arbitrarily complex and evolving persistent data. Kala is highly
efficient and secure. Kala manages the visibility of persistent data
elements to its clients, thus supporting any types of transactions,
versions, access control, security, configurations. Kala does not
restrict you to any particular model. Kala provides the mechanism, but
imposes no policy. Usable as either a link library communicating to a
server or as a standalone, Kala is compact and simple.
Kala is used for applications such as: kernel of DBMS products,
substrate for extended file systems, implementation of language
persistence, data manager for groupware applications as well as
applications which deal with large, complex, and changing volumes of
data (text databases, financial distributed transaction systems). Our
current customers use Kala in applications ranging from CASE
repositories to CAD systems, from document management for financial
institutions to OODBMS platforms, from real-time applications to
database research.  Kala is a component of broad reuse.
Motivation
The simplest persistent data storage available to you is the file
system on your disk drive. File systems have some attractive
characteristics; their performance is good, they can hold any data,
they're easy to use, and, of course, the price is right. Conversely,
files are unreliable.  They provide no mechanism for in maintaining
data consistency and only primitive data sharing facilities. Few file
systems offer version control and all require that you transform data
between "internal" and "external" forms all the time.
Unlike a file system, a true database management system provides
mechanisms for sharing data and for ensuring the integrity of the
data.  It supports transactions and version control, although the
specifics of these functions may not be exactly what your application
needs. Finally, a database system is scalable, and much more robust
than a file when your hardware or software fails.
The downside to a database system is that, compared to a file system,
it is slower by an order of magnitude or more. Also, a database system
generally confines you to dealing only with the kind of data that it
can handle. In addition, a database is usually very complicated,
difficult to learn and use, and expensive, both in terms of your cost
of operation and in the amount of system resources they consume.
Whether you choose a file system or a database manager, then, you
have to sacrifice either economy or performance. Is there a happy
medium?  Something with the speed and flexibility of files, the
reliability, shareability and robustness of databases, and at a cost
that won't break your wallet or the available hardware? Sure there is!
Kala is a first in a new breed of products, persistent data servers,
aimed squarely at the yawning gap between DBMSs and file systems.
Overview
Kala is *not* a DBMS. Instead, you use Kala whenever the few canned
combinations of DBMS features do not meet the needs of your
application. A DBMS product constrains you to accept *its* choice of
an end-user graphical interface, a query language binding, a specific
high level data or object model, a particular transaction model, a
single versioning scheme, etc. This either compromises your
application's functionality, or forces your to spend substantial
development effort and money to bridge the impedance mismatch to the
application.  Instead, Kala allows *you* to develop no more and no
less than the functionality you need. You build your domain specific
functionality our of a small set of primitives with very little code.
Your gains in productivity, efficiency, and flexibility are
substantial.
To sustain this level of flexibility and reuse, Kala manages any data
that you can represent in machine memory out of bits and references.
Examples include records, dynamically linked graphs and lists,
executable code, and object encapsulations.
Kala can handle data as small as one bit, and as large as the virtual
memory and more, while being totally unaware of the data's semantics.
Its stores and retrieves data efficiently, and compactly over a
distributed and dynamically reconfigurable set of Stores. Upon
retrieval, Kala dynamically relocates embedded references to retain
the original topological structure of the data, thus preserving
referential integrity. Kala also supports active data, physical store
management, and automatic archiving.
Kala repackages the fundamentals and universals of data management in
one reusable data server, separating them from the application domain
specific models and policies. Kala defines a low level interoperabi-
lity point for the data storage domain, just as X does for the display
domain and Postscript does for the printing domain.
Kala has matured through four successive versions to its present
industrial strength implementation and stable API. Kala is lean,
compact, and portable. Kala is a high performance, low overhead
system. We call it a Reduced Instruction Set Engine (RISE). Unlike
large, complex, and typically bulky DBMS products, Kala is small,
simple, and suitable for managing anywhere from a single diskette to
terabytes of distributed data.
Benefits
* For those who need functionality traditionally associated with
  databases, but cannot tolerate the overhead and complications DBMS
  products introduce, Kala offers a flexible, compact, performant,
  elegant, and simple alternative.
* For those whose application domain requires data models where the
  mapping to those offered by today's DBMS products is cumbersome,
  introduces development and execution overhead, and is not portable
  across multiple linguistic and environmental platforms, Kala offers
  a data model independent interface against any data model
  expressible in terms of bits and pointers can be easily built.
* For those who need DBMS functionality or qualities that no single
  DBMS product now has, Kala offers the opportunity to build that
  functionality now with little effort out of a simple set of
  primitives, and not wait for one vendor or another to deliver
  it later.
* For those who have determined that the only viable option for their
  application's persistent data needs is the file system, and have
  resined to the idea that they will have to build everything else
  they need from scratch, Kala offers an off-the-shelf implementation
  without loss of any of files' advantages.
* For those who need performance, size, portability, storage
  compactness, and industrial strength that no single DBMS product can
  now satisfy, Kala offers all of the above now.
* For those who realize that while object-level interoperability is a
  strong desideratum, the likelihood of a single, universal such model
  in the foreseeable future is quite low, Kala offers a solid, long
  term alternative. Data store interoperability that brings us beyond
  file systems is the best practical bet. Kala is the basis for data
  store interoperability now.
* Finally, for all of you who are concerned about the economics of
  software, and take the view that there are many elements that
  could contribute negatively to the soundness of your business, such
  as operational costs, software maintenance costs, software licensing
  costs, software development and learning costs, etc., you will find
  Kala an economically sound, sensible, and practical product.
Features
- The execution architecture is that of multiple (communicating)
  servers and multiple clients. Kala can also be configured in a
  standalone (single process) mode. Kala's IPC is built for maximum
  performance, portable to any given datagram protocol.
- The managed data elements are made out of uninterpreted bits and
  references. Data elements (named `monads') are universally uniquely
  identified. Bits are stored with no overhead. References,
  represented in memory as native machine pointers, are stored
  very compactly, introducing an average of 2.5 bytes overhead.
- Kala is a fully recoverable system, short of media damage. Recovery
  from hardware failures can be supported by the layer beneath Kala.
- The Kala primitives support arbitrary transaction models, including
  classic short transactions, long (persistent) transactions, nested
  transactions, shared transactions, pessimistic and optimistic
  policies, etc. Concurrency control is achieved through two locking
  mechanisms (short-term and long-term (persistent, shared) locking),
  with full support for atomicity of operations and two-phase commit.
- The Kala primitives support arbitrary versioning models, allowing
  versions to co-exist in split/rejoined networks, various version
  organization strategies (single-thread, tree, DAG, etc.). Kala
  primitives provide mechanisms for arbitrary access and update
  triggers, such as notifications, security checks upon access/update,
  etc. __ with no limitations on what the trigger code does. Kala
  provides protection measures against virus and other intruding
  executions.
- The Kala primitives support a wide range of access control, security
  and protection models, including revocable access rights, access
  control without the overhead of ACL management, arbitrary access
  validation routines, etc. Kala does not introduce any more security
  holes than the operating environment already has.
- Kala has primitives for physical store allocation and de-allocation
  management, for a wide spectrum of store administrative tasks, as
  well as licensing administration. The latter includes application-
  sensitive time-limited client-connect-based licensing, as well as
  metered (connect/load/store) usage. Kala can be set up to do
  automatic archiving and backup of its physical store.
- Kala provides a wide spectrum of licensing schemes, usable by
  platforms and applications built upon Kala to their customer base.
  Kala provides renewable licenses, perpetual licenses, full
  protection against duplication without hardware (hostid) support,
  metered (pay-by-use) usage, etc.
- And more ... not fitting on this page-long Technical Brief.
Availability
o Kala is available now on Sun platforms (SunOS / 68K & SPARC), as
  well as on 80x86/MS-DOS (both Microsoft and Borland compilers &
  runtimes supported) platforms. If you are interested in a port to
  your favorite platform, call us to discuss our Development and
  Porting Partnership Programme.
o Kala's interface is ANSI C, also callable from C++. If you are
  interested in an interface or a binding to your favorite programming
  language, please call us to discuss out Development Partnership
  Programme.
o For pricing and other information, please contact us by phone, fax
  or via e-mail at Info@Kala.com
 _     _     ____   _         ____ tm ____________________________________
 \\   /     |    \   \       |    \       \\\\
  \\ /__     \ __ \   \       \ __ \       \\\\
   \\    \    \    \   \       \    \       \\\\
    \\    \    \    \   \       \    \       \\\\  No more than you need !!!
     \\'   \'   \'   \'  '____'  \'   \'      \\\\  No less than you want !!!
      ........................................................................
      Penobscot Development Corporation                 email: Info@Kala.com
       One Kendall Square Building 200 Suite 2200 Cambridge MA 02139-1564 USA
        voice +1-617-267-KALA fax +1-617-859-9597 tech support +1-201-539-7739
         ...............(5252) fax +1-617-577-1209.............................
     +---------------------------------------------------------------+
     |   Copyright (c) 1992-93, Penobscot Development Corporation.   |
     |   Kala is a Trademark of Penobscot Development Corporation.   |
     +---------------------------------------------------------------+
On Schema Evolution (from original survey):
Kala manages an untyped persistent store, implementing the semantics
of robust, distributed, secure, changing, and shareable persistent
data.  Layers built upon the Kala platform can implement the semantics
of objects with the same properties.
As it operates below the schema layer, Kala does not address schema
evolution directly. However, It supports the building of schema'ed
layers above it and below the application, and those layers can
provide for schema evolution conveniently using Kala primitives.
This parts-box approach requires extra work on the part of the developer
compared to out-of-the-box solutions, but provides power and
flexibility sufficient for relatively low cost solutions in
difficult environments (e.g. graph-structured data, dynamic classing)
where no out-of-the-box solution is available.
Contacts:
Sergiu Simmel           sss@kala.com
Ivan Godard             ig@kala.com
general information     info@kala.com
subscription to moderated newsletter    forum-request@kala.com
REFERENCES:
        Segui S. Simmel and Ivan Godard. "The Kala Basket: A
        Semantic Primitive Unifying Object Transactions,
        Access Control, Versions, annd Configurations

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