# Appendix A
Glossary

This chapter gives descriptions for Replication Specific terms that are used in this manual.

Administration Server
  An Administration Server is a component of an Empress Server which handles its administrative requests.
Empress Replication
  Empress Replication is the process of creating a set of tables as replicates (copies) of a single master table and their synchronization to the current state of the master table. Typically, the set of tables live in separate databases in separate locations.
Empress Servers
  Empress Servers are "Empress Replication Master Server" and "Empress Connectivity (ODBC) Server". Empress Servers handle requests from clients, perform server-side operations and control the flow of information between the clients and their appropriate servers. The administrative operations of Empress Servers are controlled by Empress Server Administration Utility. Operations performed by an Empress Database Server are not in the scope of this Manual.
Master Table (or Master)
  A Master Table is an update-able database table that serves as the source of data for a Replication World. A Master Table has some restrictions regarding to a normal database table, and is update-able by the applications and users having necessary privileges.
Original Master Table
  A Replication World is formed when a Normal Table is converted to a Master Table. This Master Table is called Original Master Table. The Original Master Table Access Information (i.e. its host name, database name and table name) and its creation timestamp construct the Original Master Table Information. The Original Master Table Information uniquely indetifies a Replication World. A Replicate Table automatically inherits Original Master Table Information from its RMT. Original Master Table Information is always constant for a Replication World, even if Original Master Table does not exist, or does not serve as Master Table anymore.
Purging
  Purging is physically deleting a record from a database table, when deleted records of a Master Table are only marked as being deleted. These marked records are Purged only after their data is synchronized with the replicates of their table. Note that the records marked as "Deleted" are considered as deleted records, and are only used internally for Replication purposes.
Record Timestamp
  This is the latest timestamp that a record has been modified.
Replicate Table (or Replicate)
  A Replicate Table is a read-only database table that gets the copy of data which is updated in Master Table. A Replicate Table has some restrictions regarding to a normal database table, and is not update-able by the applications and users. The only updates to a Replicate Table are done through Replication Synchronization with its Replication Master Table.
Replication Master Entry
  Each Replication Master Entry contains information to a access to a candidate Replication Master Table which is a combination of Replication Master Server name, database name and table name. Replication Master Entry also contains information about Replication Master Order, and Enabled/Disabled status of RMT.
Replication Master Order (Replication Order)
  Replication (Master) Order is the order for a Replication Master Table to be "chosen" as the Replication Master Table with which a Replication Synchronization will tried to be performed. The Order Number of the Replication Master Entry, refers to Replication Master Order for the Replication Master Table accessed by that Replication Master Entry.
Replication Master Server
  A Replication Master Server is a special purpose Empress Server that is used for replication purpose. Replication Master Server resides in RMT-Side and accesses a Replication Master Table for its replication operations. Execution of a Replication Master Server is controlled by requests sent through Empress Server Administration Utility.
Replication Master Table (RMT)
  In a process of synchronization, a Replication Master Table (RMT) is the origin of data replication for another Replication Table. It can be either a Master Table or a Replicate Table.
Replication Relation
  A Replication Relation is a logical, binary relation between a Replication Master Table RMT and a Replication Replicate Table RRT. RRT is authorized to be Replication Replicate Table for RMT, by having a Replication Replicate Entry accessing to RRT in Replication Replicate List of RMT. RMT is "claimed" to be Replication Master Table for RRT by having a Replication Master Entry referring to RMT in Replication Replicate List of RRT.
Replication Replicate Entry
  Each Replication Replicate Entry contains information to access a candidate Replication Replicate Table, which is a combination of host name, database name, table name. Replication Replicate Entry also contains information about possible Subset Replication Condition, if Subset Replication is required.
Replication Replicate Table (RRT)
  In a process of synchronization, a Replication Replicate Table (RRT) is the target of data replication for another Replication Table.
Replication Table
  A Master Table or a Replicate Table have some restrictions regarding to a normal database table, and because of this difference they are called Replication Tables.
Replication Table Switch
  A Master Table can be altered to a Replicate Table and a replicate table can be altered to a master table. The switch of replication table types to each other is called Replication Table Switch. Before a master table is switched into a replicate table, its candidate replication master table must be defined, otherwise the switching operation will fail.
Replication World
  Replication World is a combination of a Master Table, one or more Replicate Table(s) and the replication relations between these Replication Tables. A Replication World can be a combination of inter-related Replication Relations which have some common Replication Tables. In a Replication World, a Replication Table can be either a Replication Master Tables or a Replication Replicate Table, or both at the same time, depending on the Replication Relation in which it participates.
RMT-Side
  Considering a certain Replication Relation, RMT-Side is the logical position where the Replication Master Table, Replication Master Server and a Replication Replicate Entry reside. This Replication Replicate Entry is the one accessing Replication Replicate Table which is in the RRT-Side.
RMT Switch
  For each Replication Synchronization a Replication Master Table is chosen automatically, as the source of data for Replication Synchronization. RMT Switch is choosing a different Replication Master Table from the one chosen in the last Replication Synchronization. A RMT Switch is occurred from the point of view of a single Replicate Table.
RRT-Side
  Considering a certain Replication Relation, RRT-Side is the logical position where the Replication Replicate Table, Synchronization Client, and a Replication Master Entry reside. This Replication Master Entry is the one accessing Replication Master Table which is in the RMT-Side.
Service Server
  A Service Server is a component of an Empress Server which handles the service requests made to an Empress Server. There might be more than one Service Servers for an Empress Server and the number of Service Servers can be specified when starting an Empress Server and can be changed dynamically during execution of an Empress Server.
Spooler
  A Spooler is a component of Empress Server which spawns and controls an Administration Server and one or more Service Servers.
Subset Replication
  Subset Replication duplicates rows from the Replication Master Table that satisfy a predetermined condition. The subset condition is a Restricted SQL Where Clause without explicit database and table references. This Restricted SQL Where Clause allows selecting the rows from a Replication Master Table by specifying any attribute of the table, but prevents joins, sub selects, aggregate functions, and grouping clauses.
Synchronization (Replication Synchronization)
  (Replication) Synchronization is the process of updating a Replicate Table with the changed data of its "chosen" Replication Master Table since the last successful synchronization.
Table Timestamp
  Table Timestamp is the timestamp that a Replicate Table has the snapshot of its Master Table.
Timestamp
  Is a continuously increasing Standard Time. For example if Operation A is performed at Timestamp TA, and later an Operation B is performed at Timestamp TB, TA is less than TB, without considering the local time of the hosts running A and B. This is the case only for two hosts with synchronized time. Each Timestamp is an exact time containing Year, Month, Day, Hour, Minute, Second and Microsecond.