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Find details on the SPL language, toolkits, APIs, commands, and more.
Streams Processing Language (SPL)
Streams Processing Language (SPL) is a distributed data flow composition language that is used in Teracloud® Streams. SPL has primitive types, program structures, and definitions that are tailored for streaming data.
Operators
Operators process tuples in an incoming stream and produce an output stream as a result. SPL supports two kinds of operators: primitive operators and composite operators. A primitive operator is written in C++ or Java™. A composite operator is written in SPL and contains a reusable stream subgraph.
Operator invocations
The purpose of SPL is to allow users to create streams of data, which are connected and manipulated by operator invocations.
Output clause
The output clause assigns values to attributes in output tuples each time the operator submits data to an output stream.

Welcome
Learn about the core capabilities of Teracloud® Streams, its architecture, and key concepts.
Installing
Use this information to install, upgrade, and uninstall the Teracloud® Streams product.
Configuring
Create a basic or an enterprise domain which is a single point for configuring and managing common resources, security, and instances.
Administering
Administer the product by using the Teracloud® Streams graphical user interface, APIs, or the streamtool command-line interface.
Developing
Develop stream applications with the Streams Processing Language (SPL), Java, and Python.
Troubleshooting
Resolve problems with Teracloud® Streams using the troubleshooting tools provided with the product as well as the resources offered by Teracloud Support.
Reference
Find details on the SPL language, toolkits, APIs, commands, and more.
- APIs
  Application programming interfaces (APIs) provide functions that simplify applications development.
- Job configuration overlays
  You can specify or change configuration parameters when you use the submitjob or updateoperators operations. The settings control submission constraints, host constraints and locations, and operator status. Parameters are captured and updated in the configuration JSON file. When you change the values in the job configuration overlay file, the changes override any previously set values.
- Commands
  Teracloud® Streams provides a number of commands you use to perform tasks.
- Operator model
  An operator model is an XML document that describes the basic properties of a primitive operator.
- Streams Processing Language (SPL)
  Streams Processing Language (SPL) is a distributed data flow composition language that is used in Teracloud® Streams. SPL has primitive types, program structures, and definitions that are tailored for streaming data.
  - Language overview
    SPL contains types, expressions, statements, functions, clauses, and other elements of a programming language.
  - Grammar notation
    This language specification adopts a flavor of Backus-Naur Form (BNF) to describe the syntax of language features.
  - Lexical syntax
    SPL defines a set of rules to determine the syntax of a program.
  - Grammar overview
    Here is the SPL grammar syntax, with references to the sections that contain the semantics.
  - Expression language
    Though SPL is a streaming language, there are many places where it uses expressions that are found in traditional imperative or functional languages.
  - Annotations
    Operators can be annotated. Annotations influence the run time behavior of stream applications.
  - Types
    SPL has several primitive types that are tailored for streaming, and a few composite types that are inspired by scripting languages but statically checked. The following topics describe the types, how to define them, and how to convert values between different types.
  - Operators
    Operators process tuples in an incoming stream and produce an output stream as a result. SPL supports two kinds of operators: primitive operators and composite operators. A primitive operator is written in C++ or Java™. A composite operator is written in SPL and contains a reusable stream subgraph.
    - Operator invocations
      The purpose of SPL is to allow users to create streams of data, which are connected and manipulated by operator invocations.
      - Operator invocation head
        The head of an operator invocation lists the output and input streams and the name of the operator that processes the data.
      - Logic clause
        The logic clause consists of local operator state that persists across operator firings, and statements that execute when an input port receives a tuple or a punctuation and thus fires.
      - Window clause
        A window is a logical container for tuples recently received by an input port of an operator.
      - Param clause
        The param clause contains code snippets that are supplied to the operator at invocation time.
      - Output clause
        The output clause assigns values to attributes in output tuples each time the operator submits data to an output stream.
      - Config clause
        The config clause specifies hints and directives that influence how the compiler builds this operator invocation, or how the runtime system executes it.
      - History
        Expressions in parameters or output assignments of operator invocations can refer directly to tuples received in the past.
    - Operator definitions
      A stream operator can be invoked to transform input streams to output streams. SPL supports two kinds of operators: primitive operators and composite operators.
  - Program structure
  - Operator config clause
    The config clause specifies hints and directives that influence how the compiler builds an operator invocation, or how the runtime system runs it.
- Toolkits
  A toolkit is a set of SPL artifacts, which are organized into a package. Toolkits make SPL or native functions and primitive or composite operators reusable across different applications.
- SPLDOC markup
  You can use SPLDOC markup in the descriptions associated with the SPL artifacts in a toolkit. The spl-make-doc command generates HTML documentation from the marked up artifacts.
Glossary
Use this glossary to find terms and definitions for Teracloud® Streams.

Output clause

The output clause assigns values to attributes in output tuples each time the operator submits data to an output stream.

For example, output Sale: item = Bid.item, id = n; assigns values to the attributes item and id in the output stream Sale. The label, such as Sale, is an output stream name or alias, and opens the scope of that stream similarly to a Pascal with statement. The result is a comma-separated list of assignments to attributes.

Most operators have the auto-assignment flag set in the operator model, meaning any attribute in the output stream that is not assigned by the output clause is implicitly copied from an attribute with the same name and type that is defined on an input stream. To find the matching attribute, the compiler searches all attributes that start with port 0 and proceeds until a match is found or all ports are checked. Certain operators might have different forwarding behavior, which is specified by their operator model. For more information about operator models, see Compile-time APIs.

Some operators, such as the Aggregate operator in the standard toolkit, define custom output functions, such as Sum, that are in scope in their output clause. Such custom output functions can be only used in top-level expressions. For example, sum = Sum(i) is correct but sum = (int32)Sum(i) is an error, because it is nested in a cast expression.

Tip: Avoid calling stateful functions in the output clause, since this clause is a confusing place to inject side effects or non-determinism.