Concepts and Definitions
The purpose is to collect concepts and definitions for group documentation. Requirements will be collected separately, please aim for compact but unambiguous definitions.
Scope of the Community Group
Between November 2013 and April 2014 the community group focuses on representation and continuous querying of streams consisting of RDF elements of time-varying data annotated by a minimum of one timestamp or interval, where the timestamp may be implicit based on the reception time of the object.
RDF Streams
RDF Stream: A potentially infinite sequence of time-varying data elements encoded in RDF [1]
Elements in An RDF Stream
Streaming object: A separable data element, which is transmitted in a stream. The object may contain zero or more timestamps t and zero or more time intervals [ t(start) , t(end) ) to annotate the object and the validity of the included data.
Static Object: A streaming object consisting only of static fact(s) considered valid until redefined.
Note: In the first phase of the group only streaming objects carrying time-varying data are considered, i.e. static object are out-of-scope.
Actors in a Stream Processing System
Stream producer: Originator, source of a stream.
Stream consumer: Receiver, sink of a stream.
Stream processing agent: A software module, which accepts one or more streams as input, performs computation and produces one or more streams as output.
Other
Mikko: This section has become a collection of definitions, which are good and practical, but not strictly necessary in describing streams.
Recorded Data stream: A stream saved e.g. to a computer file. Characterized by:
- Possibility for non-realtime (faster / slower) processing
- Possibility for repeated processing of the same stream
- Need for explicit time information for streaming objects (either in the streaming objects themselves or specified for the whole stream), unless the elements are static objects.
- Finite length with both a beginning and an end.
Stream processor: A software program, which accepts one or more streams as input and performs computation.
Temporally valid fact: A fact with a known validity period expressed as a time interval [ t(start) , t(end) ). Incorporated in state objects.
Other names: situation, state
Static fact: Static knowledge, which can be expressed as RDF triples. Infinite validity.
Other names: Static (or slowly evolving) knowledge; stored data.
State object: A streaming object describing a set of temporally valid facts including a known validity period expressed as a time interval [ t(start) , t(end) ).
Event object: A streaming object describing anything that happens, or can be contemplated as happening. Characterized by instantaneous occurrence represented by a single point in time. Time may be implicit based on the time of occurrence of the object in the (live) stream.
"Derived event": An event that summarizes, represents, or denotes a combination of zero or more events, temporally valid facts or static facts such that there is always at least one triggering event object or temporal fact to establish the time of event occurrence.
Mikko: This is an extension of the "complex event" definition to cover the use of temporal facts and facts as inputs. Event Processing Glossary v2 complex event definition covers only events (simple or complex) as inputs.
"Derived state": A state that summarizes, represents or denotes a combination of one or more states, zero or more static facts and zero or more events.