Extensible Stylesheet Language Formatting Objects - Introduction to XSLFO
XSLFO is
Extensible Stylesheet Language Formatting Objects which is an XML document
by itself. This is a language for formatting XML data and is a W3C recommendation.
This is interchangeably also called as XSL.
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The XSLFO
documents are more complex when compared to XSLT. The XSLFO documents
contain formatting information that is used to format the XML data in
the desired format. For example, the pagination, layout and other formats
required for the XML documents are found in the XSLFO document. Since
XSLFO documents are more complex, usually XML documents are initially
transformed into formatting documents and then finally using some tools
available, the XSLFO document is converted to give an output format.
The XSLFO
documents will usually have a file extension of .fo or .fob. To make it
easier to open them in the XML editors some developers used to have these
file’s extension as .xml itself. But it is a practice to have their
extension as .fo or .fob. The code given below is an example of an XSLFO
document.
<?xml
version="1.0" encoding="utf-8"?>
<fo:root>
<fo:layout-master-set>
<fo:simple-page-master master-name="MasterMain">
<!-- The page template can be given here -->
</fo:simple-page-master>
</fo:layout-master-set>
</fo:root>
The XSLFO
document has a root element called the <fo:root> which is the starting
element of the document. Since this is an xml document, it is proper to
start the document with the xml declaration. You can specify the xml namespace
for the xslfo document in the root node itself, i.e., in the <fo:root>
itself as an attribute. After this root element you have the layout-master-set
element which contains the simle-page-master element. Within the layout-master-set
element you can have any no of simple-page-master elements. These simple-page-master
elements contain the page template that is required to give the desired
output to the xml data.
The simple-page-master
will have an master-name attribute which identifies the simple-page-master.
It contains the page formatting details in the form of attributes. The
code given below gives a sample of the simple-page-master with those attributes.
<fo:simple-page-master
master-name="MasterMain"
page-height="20cm"
page-width="15cm"
margin-left="1cm"
margin-right="1cm"
margin-top="1cm"
margin-bottom="1cm">
<!--
The page template can be given here -->
</fo:simple-page-master>
The attributes
that are given in the above code are page-height, page-width, margin-left,
margin-right, margin-top, and margin-bottom which are specified in cms.
These attributes are self describing and does not need explanations.
Apart from
the layout-master-set in the root element, there is another element called
the page-sequence which contains the page contents in it. The page sequence
has an attribute called master-reference which refers to the master-name
of any page template. The following code gives the structure of the page-sequence
element.
<fo:page-sequence
master-reference="MasterMain">
<!— Content of the page is given here -->
</fo:page-sequence>
The formatting
model of XSLFO defines different areas for the output of the document.
The output is split into different areas. The areas are: Pages, Regions,
Block Areas, Line Areas, and Inline Areas. The output of any document
in this formatting model has many pages. Pages are split into Regions
and Regions are split into Block Areas. A Block Area can have other block
areas or Line Areas. Line Areas contain Inline Areas, which contain the
actual text or image of the document.
<fo:page-sequence
master-reference="MasterMain">
<fo:flow flow-name="MainFlow">
<fo:block>
<!—Page Content is given here -->
</fo:block>
</fo:flow>
</fo:page-sequence>
The code
given above gives the actual structure, where the page content is given.
Within the page-sequence element, there is an element called the flow.
This flow element has a block element which contains the actual content
that comes in the page.
<fo:block
font-size="20pt">
Block Heading
<fo:inline font-style="italic">
Sub-Heading
<fo:inline font-weight="bold">Content Here...</fo:inline>
</fo:inline>
</fo:block>
A <fo:block>
element can also have many <fo:inline> elements within them as given
in the above code. It is also possible that the inline elements can contain
other inline elements. As we have said earlier the block elements can
also contain other block elements and the structure of the document can
be more complex. XSLT is combined with XSLFO to produce quality and fast
output. An XSLFO document needs programs to convert the document into
a quality ouput like pdf document or html document. There are many software
available for this purpose. Softwares like XSL Formatter, Xinc, and Scriptura
are used to convert the XSLFO documents to other types of document outputs.
Software such as XML2PDF (Microsoft .Net Framework based engine) and Sigmagis
are also used for the conversion of XSLFO documents.
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