SQL/MX 3.2 Management Manual (H06.25+, J06.14+)

when accessed by their ANSI names on remote nodes. Similarly, the metadata definitions for a
database object, identified by its ANSI name, can be located and retrieved regardless of where
that database object's metadata definitions are located in the network.
For location-independent ANSI names, ANSI name lookup always starts with the CATSYS and
SCHEMATA system schema tables on the local node. Next, the node that contains the metadata
definitions for the ANSI-named object is identified. For SQL/MX Release 3.x, that node must have
the automatic catalog reference for the object's catalog. The location of the node can be identified
from the CAT_REFERENCES table of the system schema of any node on which the object’s catalog
is registered. The remainder of the lookup involves using the catalog’s definition schema tables on
the automatic catalog reference node.
Visibility Rules
Distributed database objects can be accessed from a node only if the objects are visible on that
node.
For SQL/MX Release 3.x, these visibility rules govern all access to database objects and metadata
in a distributed database environment:
• A database object on one node is visible on a remote node only if a catalog reference for
the object’s catalog has been registered on that node. The affected catalog, including all
schemas and database objects within it, is then visible from that node.
• A database object can be distributed only to remote nodes where its catalog has been
registered.
• A database object—or a partition of the object—can be opened only if that object’s catalog
is visible on the node of the opener.
• To avoid visibility anomalies, related catalogs must have identical visibility. This rule affects
statements or commands that establish a relationship between catalogs, such as a CREATE
VIEW statement that references tables from two or more catalogs in the view’s query text.
Although their names are similar to ANSI names, the compiled modules in OSS directories are not
subject to these visibility rules.
Transparency
The use of distributed databases is transparent to users and applications except for statements,
commands, and syntax that directly manage the distribution. When the objects in a user catalog
created on one node are visible to other nodes, there are no limitations on what those other nodes
can do with the catalog’s objects. The other nodes can execute DML and DDL statements and utility
commands on the objects just as the original node can.
Because of transparency, users need not be aware of what node they are executing on or where
metadata or user data is located.
Security Guidelines
• Access to a remote node in an Expand network—including access to distributed SQL/MX
database objects and registered catalogs—requires successful remote password validation.
• Successful remote password verification is also required for the executing user ID of any
command that creates or accesses metadata or user data on a remote node or that starts a
process on a remote node.
• The security mechanisms enforced for ANSI objects on the local node are also enforced for
distributed ANSI objects.
• Only the person who creates and owns the catalog or the local super ID user can register or
unregister catalog references from nodes.
266 Managing an SQL/MX Distributed Database