Glossary

action

An action is a block of EPL code. Optionally, an action can have parameters and/or a return type. An action can be called, typically as part of responding to an event listener. Actions can be members of monitors or events. The following action names have special meanings and may be called by the correlator:

• On monitors only: onload(), ondie(), onunload()

activation

In EPL streams, an activation is when the passage of time or the arrival of an item causes a stream network or an element in a stream network to process items.

aggregate function

A function that operates on all items in a stream query window, for example, sum().

batch

When you define a window in a stream query, you can specify that you want to update the window in batches. A batch can be a certain number of items, or it can be the items that arrived in a certain length of time.

bundle

A bundle is a named collection of Apama-provided files that can be added to an Apama application. A bundle can include EPL files, event files, and configuration files.

.cdp

File extension for Apama correlator deployment packages.

CEP

Complex event processing. CEP technologies let you detect and process events derived from other events, and sequences of events with or without temporal constraints.

channel

A channel is a string name that contexts and receivers can subscribe to in order to receive particular events. In EPL, you can send an event to a specified channel. Sending an event to a channel delivers it to any contexts that are subscribed to that channel, and to any clients that are listening on that channel.

connectivity plug-in

A C++ or Java class running inside the correlator that can transform and transmit messages between the correlator and external data sources.

context

Contexts allows EPL applications to organize work into threads that the correlator can concurrently execute. In EPL, context is a reference type. When you create a variable of type context, or an event field of type context, you are actually creating an object that refers to a context. The context might or might not already exist. You can then use the context reference to spawn to the context or enqueue an event to the context. When you spawn to a context, the correlator creates the context if it does not already exist.

correlator

The event “correlation” engine at the heart of Apama. The correlator looks for events of interest, analyses matching events, and executes appropriate actions.

correlator deployment package

A correlator deployment package (CDP) is a file that contains application EPL code in a proprietary, non-plain-text format. These files treat EPL files similarly to the way Java files are treated in JAR files. CDP files can be created using the engine_package utility. CDP files can be injected to the correlator.

current events

The set of current events contains the events in the window(s) of a partition.

EPL

The Apama Event Processing Language (EPL) is an event-based scripting language that is an interface to the correlator.

EPL plug-in

EPL plug-ins are C++ code modules, Java classes or Python programs that you write to extend the capability of an Apama component.

event

An occurrence of a particular circumstance of interest at a specific time that usually corresponds to a message of some form. The message is a collection of attribute-value pairs that describe a change in an object.

event listener

An EPL event listener observes the correlator event stream, analyzing each event in turn until it finds a sequence of events that match its event expression. When this happens, the event listener triggers, causing the correlator to execute the listener action. See also stream listener.

event pattern

Specification of the event or sequence of events or aggregation that you are interested in. An event pattern can include conditions and operators.

event template

Basic unit of monitoring in the correlator. An event template specifies the pattern that you want to act on. A simple application contains one or a few event templates. A more complex application can contain many event templates. Here is an example of the data that a particular event template might define:

• Instrument = IBM
• Bid Price > 93 and < 95
• Offer Price = *
• Bid Volume > 100000
• Offer Volume = *

.evt

File extension for files that contain events.

exception

An exception is an object that represents a runtime EPL error that can be caught with a try... catch statement. In EPL, Exception is a reference type in the com.apama.exceptions namespace. See Exception handling.

listener

See event listener and stream listener.

lot

In EPL stream, a lot means the items produced by a single activation of a stream query. Like an auction lot, a stream query lot can contain one or more items.

MemoryStore

The MemoryStore provides an in-memory, table-based, data storage abstraction within a correlator. All EPL code running in a correlator in any context can access the data stored by the MemoryStore. In other words, all EPL monitors running in a correlator have access to the same data.

method

There are two kinds of built-in methods: type methods and instance methods. Type methods are associated with types. Instance methods are associated with values. Built-in methods are treated exactly the same as user-defined actions. See action.

.mon

File extension for EPL files.

monitor

A monitor contains event monitoring patterns and the responses to take when the monitor’s listeners detect those patterns. You use EPL to define a monitor.

MonitorScript

This is an older term for EPL, the language at the heart of Apama.

optional

An optional is an EPL value that contains either a value (of some EPL type), or is empty and thus has no value. This is useful for mapping to null values in other languages such as Java, or for data which may not be present in some circumstances.

partitioning

A strategy to scale Apama by deploying multiple correlator processes to spread the workload across several processors and/or machines. A correlator can be used to partition incoming events, sending them to different correlators based on rules specific to your partitioning strategy.

stack trace element

A stack trace element is an object that describes an entry in the stack trace. A com.apama.exceptions.Exception object contains a sequence of stack trace elements that show where an exception was first thrown and the calls that lead to that exception. In EPL, com.apama.exceptions.StackTraceElement is a reference type. See Exception handling.

static action

A static action can only be declared inside an event type. It does not apply to a specific instance of an event.

stream

An EPL concept for a conduit through which items flow. An item can be an event, a location type or a simple type (boolean, decimal, float, integer, or string). The set of items flowing through the stream is often referred to as “a stream of items” and so, here, a stream represents an ordered sequence of items over time. A stream transports items of only one type. Streams are internal to a monitor.

stream listener

A construct that continuously watches for items from a stream and invokes the listener code block each time new items are available.

stream network

A network of stream source templates, streams, stream queries, and stream listeners. The upstream elements in the stream network feed the downstream elements to generate derived, added-value items.

stream query

A query that the correlator applies continuously to one or two streams. The output of a stream query is one continuous stream of derived items.

stream source template

An event template preceded by the all keyword. It uses no other event operators. A stream source template creates a stream that contains events that match the event template.

window

When working with streams, a window is a dynamic portion of the items flowing through a stream. A window identifies which items a stream query is currently processing.