Glossary

Data Life Cycle Object (DLCO)

The Data Lifecycle Object manages the runtime data that is required during the execution of one PFDL-File. It is dynamic, which allows variables and tasks defined in the PFDL to be instantiated, updated and deleted during runtime.

Execution Engine

The Execution Engine (EE) provides an interface that connects the PFDL Scheduler to the Field Level Devices.

Field Device

The Field level constitutes the lowest level of the automation pyramid and captures all kind of devices that are found in industrial manufacturing systems. These devices are either sensors or actors and directly influence processes by measuring data or performing an arbitrary step of a manufacturing process.

Lexer

In lexical analysis using a lexer, the input characters of a source program are read in and then converted into a sequence of tokens. A token represents certain key words of the language or a sequence of input characters. This consists on the one hand of a token name and on the other hand of the text or the sequence of input of input characters that correspond to the token type. Within the parser, the token name is used to define the syntax of the language.

Parser

A parser receives the generated tokens of the lexer and checks whether the sequence of token names can be generated via the grammar of the language. The syntax of a language is usually defined with the help of a context-free grammar. A tree structure (syntax tree or parse tree) is usually generated at the end of the parsing process.

Petri Net Generator

The Petri Net Generator is a module in the scheduler which receives an instance of the domain model of the PFDL and transforms it into a Petri Net.

Petri Net Logic

A module in the scheduler which handles the execution of the petri net and the firing of events from outside (e.g from the execution engines).

Scheduler

The scheduler comprises almost the complete execution of a production order including the parsing of the PFDL description, model creation and validation and execution of the petri net. It interacts with the execution engines and informs them about services or tasks which started or finished.

Semantic Validation

In the semantic validation process the scheduler validates the static semantic of the instance of the domain model of the PFDL. These errors can not be detected while parsing and have to be checked additionally.

Service

A Service in the PFDL corresponds to a service in a service oriented architecture. In the context of production and manufacturing a Service-call can be used to invoke a service of a field device of the factory floor.

Task

A Task is an executable unit which executes the statements within it sequentially. Instructions in a task can be service calls, calling other tasks and various control structures. A single Task can represent the whole production order or parts of it.

Visitor

The visitor design pattern describes a procedure to interact with objects in a composition. Methods can be encapsulated, which are executed on elements of an object structure. In the context of this project, the structure is the syntax tree generated by the parser. It can be determined in which order the nodes of the syntax tree are run through. This makes flexible traversal possible and it can be chosen which nodes of the syntax tree should be visited (which information is accessed).