# 36. Glossary of AMPS Terminology

Term | Definition
--- | ---
acknowledgment | a networking technique in which the receiver of a message is responsible for informing the sender that the message was received. In AMPS: Commands to the AMPS server from an application are asynchronous: AMPS responds with acknowledgment messages to indicate the results of the command. An application acknowledges messages from an AMPS queue to indicate that the message has been fully processed, and AMPS can remove the message from the queue.
authentication | the process of establishing a proven identity for a connection to AMPS.
conflated topic | a copy of a SOW topic that conflates updates on a specified interval. This helps to conserve bandwidth and processing resources for subscribers to the conflated topic.
conflation | the process of merging a group of messages into a single message. For example, when a particular record in the SOW is updated hundreds or thousands of times a second, conflation can enable an application to receive the most recent update every 300ms, reducing the network traffic to the application while still guaranteeing that the application has recent data.
delta | a message that contains only the differences between the previous state of a stored message and the new state of the stored message. AMPS supports delta messaging for both publish (changing a subset of fields in a message) and subscribe (receiving only the fields of a message that have changed).
entitlement | the process of assigning permissions to a connection based on the identity established for that connection.
expression | a text string that produces a specific value. AMPS uses expressions in filters and when constructing fields for enrichment or projecting views.
filter | a text string that is used to match a subset of messages from a larger set of messages. In AMPS, every filter is an AMPS expression that returns TRUE or FALSE.
message expiration | the process where the life span of records stored are allowed limited.
message type | the data format used to encapsulate messages. Each message within AMPS has a single, defined message type. Each connection to AMPS uses a single, defined message type.
oof (out of focus) | notification to a subscriber that a message which was previously a result of a SOW or a SOW subscribe filter result has either expired, been deleted from the SOW or has been updated such that it no longer matches the filter criteria.
replication | the process of duplicating the messages stored into an AMPS instance to one or more additional AMPS instances
replication source | an instance of AMPS which is the receives a published message from an application, and then sends the message directly to one or more other AMPS instances (the replication destinations).
replication destination | an instance of AMPS that is receiving messages directly from another AMPS instance (the replication source).
slow client | a client that is being sent messages at a rate which is faster than it can consume, to the point where AMPS detects that the network buffer to the client has filled
SOW (State of the World) | the last value cache used to store the current state of messages belonging to a topic.
SOW Key | a value used to identify a unique message in AMPS. For a given topic, you can configure AMPS to generate the SOW key based on content in the message, provide the SOW key on each message published, or use a SOW key generator module to programmatically create the SOW key.
topic | a label which is affixed to every message by a publisher which used to aggregate and group messages.
transport | the network protocol used to transfer messages between AMPS subscribers, publishers and replicas.
transaction log | a history of all messages published which can be used to recreate an up to date state of all messages processed. Applications can query and replay messages from the transaction log.
view | a topic constructed by AMPS from the contents of one or more SOW topics. A view can aggregate or transform the underlying topics, and can be of a different message format than the underlying topics.