(A print quality
reproduction of this brochure is available in pdf format.)
Contents:
Overview
The emergence of powerful workstations, high bandwidth networks, and
cooperative processing based upon open systems has fundamentally altered
the environment for information management and corporate computing. Model
204 is one of the most powerful tools available for constructing interactive
applications that reference large databases. Yet, Model 204 runs exclusively
on the mainframe and embraces a centralized approach to application development.
The Model 204 customer base has amassed a huge inventory of applications
and databases. Most customers are satisfied with their Model 204 application
suites and they find it easy to add new applications. There is an increasing
tendency, however to label these applications as " Legacy Systems"
because they run on mainframes and have no apparent relevance to the workstation
dominated programming environments of the future. As organizations evolve
from SNA networks of 3270 clusters to networks of workstation LAN's, end
users are no longer satisfied with yesterday's application interfaces and
response times.
Janus is a family of products that provide integration of Model 204
databases and applications in a TCP/IP based client/server environment.
With Janus, an organization can capitalize on the power and efficiency
of User Language while migrating from a centralized, mainframe-based computing
model into a distributed client/server architecture. Janus offers general
C client support, integration of Model 204 in the SYBASE Open
Client/Server Architecture, and integration of Model 204 applications with the World Wide Web.
Janus TCP/IP Base
Janus TCP/IP Base provides all the tools necessary to access Model 204
databases and applications directly from workstations. It provides client/server
access over TCP/IP networks similar to Model 204 BATCH2-IFDIAL support.
Janus TCP/IP Base consists of three components:
- Object decks that are linked with the Model ONLINE load module to implement
high performance TCP/IP communications support.
- A Model 204 command set for defining and managing server threads.
- A C routine library that enables communications with the Model 204
ONLINE. Some of these routines can be used by programmers to write applications
that communicate and exchange data with Model 204, while others can be
used to communicate with a Model 204 ONLINE without any additional programming.
Janus Open Server
Janus Open Server allows Model 204 User Language procedures to be invoked
by Remote Procedure Calls (RPC) or Transact SQL EXEC statements. There
is no difference in the way client applications using SYBASE Open Client
Library invoke a stored Model 204 User Language procedure and a stored
Transact SQL procedure. The SYBASE client sends the name of a stored procedure
and an arbitrary number of parameters, and the Janus Open Server executes
that stored procedure and returns the requested data in Model 204 images
that appear as " rows" to the client, or as RPC return parameters.
Model 204 as a high performance server in the premiere distributed
computing environment.
- Pre-compiled User Language procedures invoked via RPC or Transact
SQL EXEC from Open Client
- Janus Open Server stored procedures are plug compatible with SQL
Server stored procedures
- $functions for retrieving RPC parameters and passing back result
" rows"
Janus Open Client
Janus Open Client provides a set of $functions that allow SYBASE Open
Client applications to be written in Model 204 User Language. The User
Language client applications send RPCs or language requests (e.g. Transact
SQL) to a SYBASE SQL Server or other Open Server and retrieve the results.
The Janus Open Client $functions support User Language applications as
clients to several different servers simultaneously. In fact, a User Language
Open Server application may also act as an Open Client application.
Model 204 User Language Procedures as clients in the SYBASE Open
Client/Server Architecture.
- Easy to use interface based on $functions and images
- Lets Model 204 legacy systems synchronize with other Open Client/Server
applications and databases.
Janus Specialty Data Store
The OmniConnect feature of Sybase's Adaptive Server provides SYBASE client applications
with the benefits of distributed programming across a wide variety of heterogeneous
data sources. Any client application that works with SQL Server can be
used without change against a Janus Specialty Data Store. Client applications are
presented with a unified relational view of the data contained in the various
sources as if the data were managed by a single SQL Server.
- Global catalog management
- Global request optimization
- SQL dialect translation
- Heterogeneous database joins
The Sybase Adaptive Server supports the Transact-SQL language, which
is a superset of ANSI SQL designed to facilitate stored procedures and
Remote Procedure Call (RPC). Clients may use stored procedures, static,
or dynamic SQL. The OmniConnect feature of Adaptive Server maintains a global
catalog comprising metadata from each of the data sources. The Adaptive Server
decomposes Transact-SQL requests into subrequests to be processed by the appropriate
data source. If the data source is not a SQL Server, the subrequests are
translated into a subset of ANSI SQL and sent as language strings
to the Specialty Data Store responsible for the data source.
The Janus Specialty Data Store accepts requests from the Adaptive
Server and parses the dynamic SQL strings. The Janus data catalog, JANCAT,
is used to verify the SQL strings and direct their translation into User
Language. The resulting User Language code is executed and the results
are transmitted back to the Adaptive Server. If a source query joins data
from multiple sources, for example a Sybase Adaptive Server and Model 204, the
join is performed at the Adaptive Server.
The JANCAT subsystem provides the DBA with a set of easy to use tools
for maintaining relational views of Model 204 files. An automated generation
mode scans a few hundred records of an indicated Model 204 file and makes
a best guess of the record types, nested tables, and so on. Simple editing
tools can then be used to refine the relational view.
JANCAT has very few restrictions on the types of Model 204 files and
groups that can be mapped. Multiple record types within a single file or
group are supported as multiple tables. Individual tables may be defined
as read-only. Nested tables need not possess a primary key field. A multiply
occurring field can be defined as multiple columns instead of nested tables.
- Sybase Adaptive Server sends language request with subset of ANSI SQL
- Janus Specialty Data Store replies with results data stream
The Janus Specialty Data Store has been highly optimized for processing repetitive
dynamic requests, of the kind frequently produced by application generators
and query tools. When a Janus server with type "SDS" is started,
a set of control blocks is allocated in above the line storage within the
Model 204 region and primed with information from JANCAT. This information
includes just the most basic information about each table in the relational
view and a directory of compiled requests.
When a language request is received from an Adaptive Server, the information
required to parse the request is completely resident in virtual storage.
This means that no I/O is required and very little CPU is consumed to validate
a request. Once a valid parse tree has been built the tree is hashed and
looked up in the resident request directory. If the request has already
been compiled and saved, its pre-compiled form is loaded from CCATEMP and
its LRU queue position is updated. Due to the small and highly specialized
nature of the compiled Specialty Data Store User Language requests, this load
is extremely efficient.
If the request is not found, it is translated into User code are then
saved in a CCATEMP page and the directory Language and compiled. The parse
tree and compiled code are then saved in a CCATEMP page and the directory
is updated. If the maximum number of requests have already been saved,
the compilation and parse tree for the least recently referenced request
is discarded.
The User Language requests created by the Janus Specialty Data Store
make use of Janus dollar functions to accept parameters and return results.
Compilations for requests that include terms of the form:
<column name> <operator> value
can be shared even when the various requests provide different values.
The request is compiled with an invocation of an initialization dollar
function that sets the percent variable used to represent the value. The
combination of these optimizations and the sharing of compilations results
in a dramatic reduction in overhead. Simple SELECT, UPDATE, and INSERT
statements can be processed with only 10% to 15% CPU penalty over pre-compiled
User Language.
Janus Web Server
Janus Web Server was written by Sirius Software to provide access to
Model 204 data and applications from web browsers. Janus Web Server allows
Model 204 to act as a web server on a TCP/IP network. Text (HTML and non-HTML),
image, and audio data can reside in Model 204 files and new applications
that access data can be written in User Language. Many existing applications
can be easily modified to interact with browsers. Furthermore, the existing
Model 204 security structures can be used for secure sections of web sites,
while other portions of a web site can be served to web browsers without
any security. All this is accomplished with a few simple commands. Furthermore,
Janus Web Server supports the SSL (Secure Socket Layer) protocol to provide
end-to-end encryption of data.
Janus Web Server does not require the use of any other web servers -
Model 204 itself is the web server. This means no new interdependencies
between Model 204 and other vendor products, no need to maintain applications
as a complex set of parameters and programs in two or more environments,
no need to leave non-secure back doors into Model 204 to facilitate web
server access, and no need to maintain multiple sets of userids and passwords
for a web server and Model 204. This is not to say that most sites won't
have web servers other than Janus Web Server, most probably will, but Model
204 won't be locked into an unnatural (for Model 204) paradigm by these
other servers.
Instead, the full power of User Language will be immediately available
to a Janus Web Server site. With Janus Web Server, User Language can send
data to a web browser with simple PRINT statements that contain either
HTML or ordinary text. Output from Model 204 commands can be routed to
a web browser with no programming at all. HTML documents generated by client
based tools can also be served by Model 204 with automatic substitution
into dynamic parts of these documents from data that is set in GTBL by
User Language. A set of $functions is provided that make it possible to
retrieve information about a browser request and to completely control
the data sent back to the browser. These $functions can return the values
of the data entered on an HTML form, the actual browser being used, the
URL used to initiate the request, and more.
Janus Web Server's ability to serve static HTML, image, and audio data
from Model 204 procedures makes it possible to maintain both the form that
initiates an application request and the application itself in the same
procedure file. Static data can also be kept on other servers and simply
be pointed at Model 204 as needed, if efficiency concerns override maintainability
concerns. Janus Web Server " redirects" make it possible to move
data to and from other web servers without changing existing hypertext
links to that data. Finally, as with all Sirius Software products, Janus
Web Server is written in assembler and is highly efficient.
With Janus Web Server, Model 204 customers can immediately take advantage
of web technology. Soon after installation, Janus Web Server can turn a
Model 204 legacy system into one of the most powerful and flexible web
servers on the Internet or an intranet.
Summary
In response to the explosion in desktop computing power, many organizations
have stated a goal of no further increase in mainframe capacity. Their
objective is to stabilize mainframe applications and to develop new applications
on networked workstation environments. Janus uniquely satisfies this objective:
- Janus provides industrial strength client/server access to Model 204
applications, making it possible to offload the presentation services and
significant additional portions of application logic. This can reduce mainframe
CPU consumption by up to 50%, providing increased capacity without costly
mainframe upgrades.
- Janus greatly simplifies the task of coexistence and provides for an
orderly migration of application development. Workstation application programmers
can use the Janus IFDIAL Library to access Model 204, or the SYBASE Open
Client DB-Library to transparently access data managed by either Model
204 or SYBASE SQL Server. This dramatically reduces the need for cross
training and allows for the most efficient deployment of both personnel
and hardware resources.
Janus runs under Model 204 version 2.1 and later, and is available under
MVS and VM/CMS operating systems.
