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Oracle7 Workgroup Server Distributed and
Replication Features

The Oracle7 Workgroup Server distributed and replication features provide a highly distributed client/server environment for the workgroups. The primary features include

Database links
Distributed queries and joins
Distributed updates with two-phase commit
Read-only snapshots
XA support
Connectivity to non-Oracle data via Oracle Open Gateway

This section introduces you to each of the preceding features. For detailed descriptions, refer to Oracle7 Server Distributed Systems, Volume I, "Distributed Data."

Database Links

Database links enable connections between Oracle databases of a distributed system. A database link defines a unique path to a remote database:

 create public database link stock using `stock.us';

stock is the name of the database link and stock.us is the path to a remote database. The three types of database links are private, public, and global. A private database link is owned and accessed by a specific user. A public database link can be accessed by any user. Both private and public database links can be created by users or DBAs. A global database link is created and managed by a global naming service, such as Oracle Names. Also, a global database link is created automatically for each database specified in Network Manager. It can be accessed by any user of any database in the network.

Distributed Queries and Joins

Once a database link is created, you can issue a distributed query to retrieve information from one or more remote tables at two or more nodes. You can also submit a query to join information from two or more remote tables. For example, the following distributed query joins information from two remote tables:

 SELECT custname, phone, orderdesc, orderamt     FROM app1.customer@market.us a, app2.order@sales.us b     WHERE a.orderno = b.orderno;

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Distributed Updates with Two-Phase Commit

The Oracle7 Workgroup Server supports distributed update transaction with a two-phase commit mechanism, which guarantees the participating nodes either all commit or all roll back the transaction. This mechanism ensures the data integrity of the databases participating in the distributed transaction.

Read-Only Snapshots

A snapshot is a copy of the entire table or a subset of a table. Read-only snapshots enable you to replicate data across Oracle7 databases; they are for queries only. You can retrieve data from read-only snapshots. The changes from a master table can propagate to its snapshot by refleshing the snapshot.

XA Support

The Oracle*XA component contains the Oracle XA library, which is an external application program interface (API) that enables global transactions to be coordinated by a third-party transaction manager or transaction processing (TP) monitor, such as BEA Tuxedo, IBM CICS, and IBM Transarc Encina. The Oracle XA library subroutines provide the means for a transaction manager to inform an Oracle database how to handle and process the transactions. When you install the Oracle7 Workgroup Server products, the Oracle XA library is installed automatically.

Connectivity to Non-Oracle Data via Oracle Open Gateway

The Oracle7 Workgroup Server supports the Oracle Open Gateway, which allows you to access data on a non-Oracle database, such as DB2 and Rdb. For example, the Oracle Transparent Gateway for DB2 enables you to access a DB2 database from an Oracle distributed database system. This process is transparent to the Oracle database users, so the users might not realize the data is from a remote, non-Oracle database. With the Oracle Open Gateway, you do not have to duplicate the data from non-Oracle databases to the Oracle database. The Oracle Open Gateway is not included in the Oracle7 Workgroup Server bundle.

When to Use Oracle7 Workgroup Server

Because of the similarities among the Oracle7 Server, the Oracle7 Workgroup Server, and the Personal Oracle7, it might not be obvious which product meets the needs of your client/server applications. This section suggests when it is appropriate to use the Oracle7 Workgroup Server and how the Oracle7 Workgroup Server meets your business and technical needs.

The Oracle7 Workgroup Server is appropriate in the following situations:

Network Protocol Support: In a small-to-medium size company, all computers might be connected together in a local area network using one or more of the following network protocols: Named Pipes, SPX/IPX, TCP/IP, IBM's APPC, and NETBIOS.

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If you want the power and functionality of the Oracle7 database, it is appropriate to use the Oracle7 Workgroup Server because it is designed and optimized in the workgroup environment, and it supports the common network protocol for the desktop and UNIX platforms.
Decision Support and Online Transaction Processing (OLTP): Oracle7 Workgroup Server brings the power of a multiuser Oracle7 database, and it integrates with a set of client/server tools to the desktop and UNIX platforms. Combining with the preconfigured initial database, the Oracle7 Workgroup Server is optimized for developing and deploying decision support and online transaction processing (OLTP) applications in the workgroup environment.
Distributed Data Access: In a large company, the Oracle7 Workgroup Server provides the flexibility, scalability, and openness for distributed workgroups in developing and deploying applications that require the distributed options. Workgroups in a distributed client/server environment require data sharing across multiple Oracle databases. The distributed options meet their needs by providing the distributed queries and updates with a two-phase commit.
The Oracle7 Workgroup Server offers flexibility to a workgroup by providing the data replication feature that allows read-only snapshots to refresh using event-based or demand-based refresh intervals. By making the Oracle7 Workgroup Server available on all the major desktop and UNIX platforms, workgroups can choose one or more platforms that fit their needs. The advantage of scalability enables you to port your Oracle applications and data to other systems and platforms transparently . It meets the needs of a workgroup that needs data to be migrated between Oracle databases. Openness means it is compliant with and supports the industry standards, such as XA, ODBC, and OLE. It also supports the Oracle Open Gateway.
Easy Central Administration: The Oracle7 Workgroup Server includes a suite of graphical database administration tools to simplify the database administration tasks . For example, the Oracle Enterprise Manager provides central administration of distributed workgroups with point-and-click graphical interface. You can start or shut down a database by clicking a single button. This advantage meets the needs of an independent workgroup that does not have a database administrator with extensive database administration experience.
With the Oracle7 Workgroup Server, database administrators can use the Security Manager to create and manage database user accounts or use the Tablespace Manager to create and size tablespaces without writing a single SQL statement. They can also schedule and automate jobs and events on one object or groups of objects. These integrated management features meet the needs of database administrators who manage multiple local and remote databases by simplifying the DBA tasks.