Building structured documents

Any structured documents can be viewed as a tree of higher-level elements (such as chapters or sections) that contains smaller elements (like subsections or lists) that each in turn contains even smaller elements (like paragraphs or list items). When using ferenda, you can create documents by creating such trees of elements. The ferenda.elements module contains classes for such elements.

Most of the classes can be used like python lists (and are, in fact, subclasses of list). Unlike the aproach used by xml.etree.ElementTree and BeautifulSoup, where all objects are of a specific class, and a object property determines the type of element, the element objects are of different classes if the elements are different. This means that elements representing a paragraph are ferenda.elements.Paragraph, and elements representing a document section are ferenda.elements.Section and so on. The core ferenda.elements module contains around 15 classes that covers many basic document elements, and the submodule ferenda.elements.html contains classes that correspond to all HTML tags. There is some functional overlap between these two module, but ferenda.elements contains several constructs which aren’t directly expressible as HTML elements (eg. Page, :~py:class:ferenda.elements.SectionalElement and :~py:class:ferenda.elements.Footnote)

Each element constructor (or at least those derived from CompoundElement) takes a list as an argument (same as list), but also any number of keyword arguments. This enables you to construct a simple document like this:

from ferenda.elements import Body, Heading, Paragraph, Footnote

doc = Body([Heading(["About Doc 43/2012 and it's interpretation"],predicate="dcterms:title"),
            Paragraph(["According to Doc 43/2012",
                       Footnote(["Available at"]),
                       " the bizbaz should be frobnicated"])


Since CompoundElement works like list, which is initialized with any iterable, you should normalliy initialize it with a single-element list of strings. If you initialize it directly with a string, the constructor will treat that string as an iterable and create one child element for every character in the string.

Creating your own element classes

The exact structure of documents differ greatly. A general document format such as XHTML or ODF cannot contain special constructs for preamble recitals of EC directives or patent claims of US patents. But your own code can create new classes for this. Example:

from ferenda.elements import CompoundElement, OrdinalElement

class Preamble(CompoundElement): pass
class PreambleRecital(CompoundElement,OrdinalElement):
    tagname = "div"
    rdftype = "eurlex:PreambleRecital"

doc = Preamble([PreambleRecital("Un",ordinal=1)],

Mixin classes

As the above example shows, it’s possible and even recommended to use multiple inheritance to compose objects by subclassing two classes – one main class who’s semantics you’re extending, and one mixin class that contains particular properties. The following classes are useful as mixins:

  • OrdinalElement: for representing elements with some sort of ordinal numbering. An ordinal element has an ordinal property, and different ordinal objects can be compared or sorted. The sort is based on the ordinal property. The ordinal property is a string, but comparisons/sorts are done in a natural way, i.e. “2” < “2 a” < “10”.
  • TemporalElement: for representing things that has a start and/or a end date. A temporal element has an in_effect method which takes a date (or uses today’s date if none given) and returns true if that date falls between the start and end date.

Rendering to XHTML

The built-in classes are rendered as XHTML by the built-in method render_xhtml(), which first creates a <head> section containing all document-level metadata (i.e. the data you have specified in your documents meta property), and then calls the as_xhtml method on the root body element. The method is called with doc.uri as a single argument, which is then used as the RDF subject for all triples in the document (except for those sub-elements which themselves have a uri property)

All built-in element classes derive from AbstractElement, which contains a generic implementation of as_xhtml(), that recursively creates a lxml element tree from itself and it’s children.

Your own classes can specify how they are to be rendered in XHTML by overriding the tagname and classname properties, or for full control, the as_xhtml() method.

As an example, the class SectionalElement overrides as_xhtml to the effect that if you provide identifier, ordinal and title properties for the object, a resource URI is automatically constructed and four RDF triples are created (rdf:type, dcterms:title, dcterms:identifier, and bibo:chapter):

from ferenda.elements import SectionalElement
p = SectionalElement(["Some content"],
                     ordinal = "1a",
                     identifier = "Doc pt 1(a)",
                     title="Title or name of the part")
body = Body([p])
from lxml import etree               

…which results in:

<body xmlns="" about="">
  <div about=""
       content="Title or name of the part"
    <span href=""
	  rel="dcterms:isPartOf" />
    <span about=""
	  content="Doc pt 1(a)" />
    <span about=""
	  content="1a" />
    Some content

However, this is a convenience method of SectionalElement, amd may not be appropriate for your needs. The general way of attaching metdata to document parts, as specified in Metadata about parts of the document, is to provide each document part with a uri and meta property. These are then automatically serialized as RDFa statements by the default as_xhtml implementation.

Convenience methods

Your element tree structure can be serialized to well-formed XML using the serialize() method. Such a serialization can be turned back into the same tree using deserialize(). This is primarily useful during debugging.

You might also find the as_plaintext method useful. It works similar to as_xhtml, but returns a plaintext string with the contents of an element, including all sub-elements

The ferenda.elements.html module contains the method elements_from_soup() which converts a BeautifulSoup tree into the equivalent tree of element objects.