This is just a quick post to introduce a pair of functions I wrote today while working on some of the Elgg 1.0 access control code.

Namely, call_gatekeeper($function, $file = "") and callpath_gatekeeper($path, $include_subdirs = true), both of which return a boolean value.

call_gatekeeper()

This function tests to see whether it has the given method/function (optionally also test that it is defined in a specified file) exists on the call stack.

The function will return true if the called by the named function (or its parent was called by the named function).

Here is an example of its usage:

function my_secure_function()
{
if (!call_gatekeeper("my_call_function"))
return false;
... do secure stuff ...
}

function my_call_function()
{
// will work
my_secure_function();
}

function bad_function()
{
// Will not work
my_secure_function();
}

To specify a method instead of a function, pass an array to $function containing the classname and method name.

callpath_gatekeeper()

This function is similar to call_gatekeeper() but returns true if it is being called by a method or function which has been defined on a given path or by a specified file.

The function accepts two parameters:

$path, which is either the full path of the desired file or a partial path. If a partial path is given and $include_subdirs is true, then the function will return true if called by any function in or below the specified path.

One of the often repeated comments that people have had regarding OpenDD was that we should do a version of it embedded in Atom 1.

I would therefore like to introduce the first draft of OpenDD over Atom, submitted for discussion.

In a nutshell, OpenDD over Atom makes use of Atom’s ability to embed other formats within the content tag and simply wraps a OpenDD element within an Atom entry with some additional data from the ODD element used in the Atom “envelope”

This seemed like the simplest solution, but let me know what you think!

I have just uploaded a PHP library for importing and exporting OpenDD documents. It is version 0.1 so it is still very much under development, but it should still be usable.

Import example

The import function accepts an OpenDD XML document and returns an ODDDocument object, which can then be iterated through to obtain access to the ODD* classes.

The XML file:

<odd version="1.0" generated="Fri, 09 May 2008 18:53:37 +0100">
<entity uuid="http://www.example.com/a" class="foo" subclass="http://www.example.com/b" />
<metadata uuid="http://www.example.com/c" entity_uuid="http://www.example.com/a" name="Squid" >paper</metadata>
<relationship uuid1="http://www.example.com/a" type="hates" uuid2="http://www.example.com/b" />
</odd>

Example code to process it:

$doc = ODD_Import($in);

foreach ($doc as $element)
print_r($element); // Just echo, but you should probably do something meaningful.

Export example

Export involves constructing an ODDDocument object and populating it with various classes, each one representing one of the OpenDD elements.

This object is then serialised.

Here is some example code:

$out = new ODDDocument(); // Create new document

$entity = new ODDEntity("http://www.example.com/a", "foo", "http://www.example.com/b");
$out->addElement($entity);

$meta = new ODDMetaData("http://www.example.com/c", "http://www.example.com/a", "Squid", "paper");
$out->addElement($meta);

$rel = new ODDRelationship("http://www.example.com/a", "hates", "http://www.example.com/b");
$out->addElement($rel);

echo ODD_Export($out); // Export


When I get a chance I’ll upload some libraries in other languages, but if you feel inclined then feel free to implement your own!

Just a quick note to join Ben in thanking Marc Canter for inviting us up to his home to discuss (among other things) the Open Data Definition.

Marc made an excellent blog post on the subject which clearly illustrates that he completely groks what we are trying to do.

We have some exciting times ahead of us, and are going to try and move this forward as fast as we can.

As always, if you want to be a part of it then please get involved!

The Elgg team are out in San-Francisco this week meeting up with some of the guys out here and talking about Elgg and ODD.

I will blog a bit more about it when I can, its been a bit mad so this is the first chance I’ve actually had to sit down at the computer since getting here (and I’m only able to do that because the combination of jet lag and the steak the size of my head I had for dinner last night has given me a case of insomnia).

I just wanted to share with you a thought that me and Ben had while enjoying the Californian sunshine inbetween meetings, namely a way to link ODD documents with OpenID.

For descovery of ODD documents, I was planning to use the meta / link approach similar to the way RSS is picked up. Now, it occurs to me that if we modify the spec slightly to say that a UUID should point to a page that can either be an ODD representation of the thing that it’s referring to or knows where to get it – i.e. has the appropriate header tag pointing to the url – then it becomes a trivial matter to turn a UUID into an OpenID URL.

Potentially quite useful.