Customizing the table(s) of content¶
In order to make the processed documents in a docrepo accessible for a website visitors, some sort of index or table of contents (TOC) that lists all available documents must be created. It’s often helpful to create different lists depending on different facets of the information in documents, eg. to sort document by title, publication date, document status, author and similar properties.
Ferenda contains a number of methods that help with this task. The general process has three steps:
- Determine the criteria for how to group and sort all documents
- Query the triplestore for basic information about all documents in the docrepo
- Apply these criteria on the basic information from the database
It should be noted that you don’t need to do anything in order to get a very basic TOC. As long as your parse() step has extracted a dct:title string and optionally a dct:issued date for each document, you’ll get basic “Sorted by title” and “Sorted by date of publication” TOCs for free. But if you’ve been a
Defining criteria for grouping and sorting¶
A criteria in this case is a method for grouping a set into documents into distinct categories, then sorting the documents, as well as the categories themseves.
Each criteria is represented by a TocCriteria object. If you want to customize the table of contents, you have to provide a set of these objects. You can do this in two different ways.
The first, simple, way is to specify a list of rdf predicates that you’ve extracted when parsing your documents. Ferenda has some basic knowledge about some common predicates and know how to construct sensible TocCriteria objects for them – ie. if you specify the predicate dct:issued, you get a TocCriteria object that groups documents by year of publication and sorts each group by date of publication.
To do this, you override toc_predicates() to something like this:
def toc_predicates(self): return [self.ns['dct'].issued, self.ns['dct'].identifier]
The second, more complicated way is to override toc_criteria() and have it return a list of instantiated TocCriteria objects, like this (equivalent to the above example, but with more possibilities for customization):
def toc_criteria(self): return [TocCriteria(binding='title', # variable binding, see next step label='Sorted by publication date', pagetitle='Documents published in %(select)s', selector=lambda x: x['issued'][:4], key=lambda x: x['issued']), TocCriteria(binding='identifier', label='Sorted by identifier', pagetitle='Documents starting with "%(select)s"', selector=lambda x: x['identifier'], key=lambda x: x['identifier'].lower())]
The label and pagetitle parameters are useful to control the headings and labels for the generated pages. They should hopefully be self-explainatory.
The selector and key parameters should be functions (or any callable – like the lambda functions above) that accept a dictionary of string values. These functions are called once each for each row in the result set generated in the next step (see below) with the contents of that row. They should each return a single string value. The selector function should return the label of a group that the document belongs to, i.e. the initial letter of the title, or the year of a publication date. The key function should return a value that will be used for sorting, i.e. for document titles it could return the title without any leading “The”, lowercased, spaces removed etc.
Getting information about all documents¶
The next step is to perform a single SELECT query against the triplestore that retrieves a single large table, where each document is a row with a number of properties.
(This is different from the case of getting information related to a particular document, in that case, a CONSTRUCT query that retrieves a small RDF graph is used).
If you’ve used toc_predicates() above, a query that selects just those properties is automatically constructed by the default implementation of toc_query. If you’ve created your own toc_criteria() implementation, you might need to override this method as well. It should return a string containing a valid SPARQL SELECT query.
It’s called with the graph/context URI for the docrepo in question, which you’ll probably want to use in a SELECT FROM <> clause.
It’s totally possible to both override toc_predicates() and toc_criteria(), and then let the default implementation of toc_query use the information from toc_predicates() to automatically create a suitable query.
Each TocCriteria object is initialized with a binding parameter. The value of this parameter must match one of the variable bindings specified in the SPARQL query.
Note to self: Do we really need the binding parameter to TocCriteria, now that the selector and key functions are provided with the entire dict of variable mappings?
Your selector and key functions expect a dict of string values. The keys of this dict must match whatever variable bindings specified in the SPARQL query as well.
Making the TOC pages¶
The final step is to apply these criteria to the table of document properties in order to create a set of static HTML5 pages. This is in turn done in three different sub-steps, neither of which you’ll have to override.
The first sub-step, toc_pagesets(), applies the defined criteria to the data fetched from the triple store to calculate the complete set of TOC pages needed for each criteria (in the form of a TocPageset object, filled with TocPage objects). If your criteria groups documents by year of publication date, this method will yield one page for every year that at least one document was published in.
The final sub-step transforms each of these TocPage objects into a HTML5 file. In the process, the method toc_item() is called for every single document listed on every single TOC page. This method controls how each document is presented when laid out. It’s called with a binding (same as used on each TocCriteria object) and a dict (same as used on the selector and key functions), and is expected to return a list of elements objects.
As an example, if you want to group by dct:identifier, but present each document with dct:identifier + dct:title:
def toc_item(self, binding, row): # note: look at binding to determine which pageset is being # constructed in case you want to present documents in # different ways depending on that. from ferenda.elements import Link return [row['identifier'] + ": ", Link(row['title'], uri=row['uri'])]
The generated TOC pages automatically get a visual representation of each calculated TocPageset in the left navigational column.