Adelia Print Engine (APE) is a document creation engine.
The engine runs in a Java environment (version 1.8 or higher).
Document creation has two separate steps:
Merge: Generation of a document in an intermediate language
This initial step involves dynamically creating a document. It requires the following to be provided:
- A set of raw data to be displayed in the document: the data model,
- A set of data layout and transformation rules: the template.
This process uses a template engine.
The principle of such an engine is to combine (or merge) a template with a data model to produce a formatted output (the result document).
The template should be seen as a skeleton of the document to produce: it contains the content layout rules for the result document and instructions (written in an engine-specific programming language) for using the data model and injecting this data into specific positions in the formatted output.
The engine executes the template with the data model to produce the result document. In general, a template programming language supports the following concepts:
- Browse the data model,
- Create programming variables and user functions,
- Manipulate text,
- Include sub-templates,
- Propose algorithm instructions like conditional evaluations, loops, etc.
The template engine used for this document creation step is Apache FreeMarker.
This is a Java engine used to produce a text output.
The templates executed by this engine are written in FTL (FreeMarker Template Language). ↑ Top of page
Transform: Document transformation
The second step involves transforming a document into the requested output format.
This means that the document provided as an input to the process cannot be directly used by the user: the document is written in an intermediate document formatting language which is independent of a given medium (screen, paper, etc.) and a given final output format (Microsoft Word, EPUB, PDF, Postscript, etc.).
The APE requires the documents provided as an input to the process to be written in XSL-FO language (eXtensible Stylesheet Language - Formatting Objects). This is a document content description and rendering XML tag language.
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The XSL-FO language is part of the XSL language, a set of W3C technologies designed for the transformation and formatting of XML data. The other parts of XSL are XSLT and XPath.
The transformation engine used for this step is Apache FOP. This is a Java engine used to transform XSL-FO documents into output formats like PDF, Postscript, PCL, PNG, etc.