--- layout: page title: ksqlDB Concepts tagline: Foundations of ksqlDB description: Learn about ksqlDB under the hood. keywords: ksqldb, architecture, collection, query, schema, window, view --- Learn the core concepts that ksqlDB is built around.
Events

An event is the fundamental unit of data in stream processing.

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Stream processing

Stream processing is a way to write programs computing over unbounded streams of events.

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Materialized views

Materialized views precompute the results of queries at write-time so reads become predictably fast.

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Streams

A stream is an immutable, append-only collection of events that represents a series of historical facts.

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Tables

A table is a mutable collection of events that models change over time.

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Queries

Queries are how you process events and retrieve computed results.

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Joins

Joins are how to combine data from many streams and tables into one.

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Time and windows

Windows help you bound a continuous stream of events into distinct time intervals.

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User-defined functions

Extend ksqlDB to invoke custom code written in Java.

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Connectors

Connectors source and sink data from external systems.

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Lambda Functions

Lambda functions allow you to apply in-line functions without creating a full UDF.

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Apache Kafka primer

None of this making sense? Take a step back and learn the basics of Kafka first.

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