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XXXVIII. Hyperwave functions
Hyperwave has been developed at IICM in Graz. It started with the name Hyper-G and changed to Hyperwave when it was commercialised (in 1996).
Hyperwave is not free software. The current version, 5.5 is available at http://www.hyperwave.com/. A time limited version can be ordered for free (30 days).
See also the Hyperwave API module.
Hyperwave is an information system similar to a database (HIS, Hyperwave Information Server). Its focus is the storage and management of documents. A document can be any possible piece of data that may as well be stored in file. Each document is accompanied by its object record. The object record contains meta data for the document. The meta data is a list of attributes which can be extended by the user. Certain attributes are always set by the Hyperwave server, other may be modified by the user. An attribute is a name/value pair of the form name=value. The complete object record contains as many of those pairs as the user likes. The name of an attribute does not have to be unique, e.g. a title may appear several times within an object record. This makes sense if you want to specify a title in several languages. In such a case there is a convention, that each title value is preceded by the two letter language abbreviation followed by a colon, e.g. 'en:Title in English' or 'ge:Titel in deutsch'. Other attributes like a description or keywords are potential candidates. You may also replace the language abbreviation by any other string as long as it separated by colon from the rest of the attribute value.
Each object record has native a string representation with each name/value pair separated by a newline. The Hyperwave extension also knows a second representation which is an associated array with the attribute name being the key. Multilingual attribute values itself form another associated array with the key being the language abbreviation. Actually any multiple attribute forms an associated array with the string left to the colon in the attribute value being the key. (This is not fully implemented. Only the attributes Title, Description and Keyword are treated properly yet.)
Besides the documents, all hyper links contained in a document are stored as object records as well. Hyper links which are in a document will be removed from it and stored as individual objects, when the document is inserted into the database. The object record of the link contains information about where it starts and where it ends. In order to gain the original document you will have to retrieve the plain document without the links and the list of links and reinsert them. The functions hw_pipedocument() and hw_gettext() do this for you. The advantage of separating links from the document is obvious. Once a document to which a link is pointing to changes its name, the link can easily be modified accordingly. The document containing the link is not affected at all. You may even add a link to a document without modifying the document itself.
Saying that hw_pipedocument() and hw_gettext() do the link insertion automatically is not as simple as it sounds. Inserting links implies a certain hierarchy of the documents. On a web server this is given by the file system, but Hyperwave has its own hierarchy and names do not reflect the position of an object in that hierarchy. Therefore creation of links first of all requires a mapping from the Hyperwave hierarchy and namespace into a web hierarchy respective web namespace. The fundamental difference between Hyperwave and the web is the clear distinction between names and hierarchy in Hyperwave. The name does not contain any information about the objects position in the hierarchy. In the web the name also contains the information on where the object is located in the hierarchy. This leads to two possibles ways of mapping. Either the Hyperwave hierarchy and name of the Hyperwave object is reflected in the URL or the name only. To make things simple the second approach is used. Hyperwave object with name my_object is mapped to http://host/my_object disregarding where it resides in the Hyperwave hierarchy. An object with name parent/my_object could be the child of my_object in the Hyperwave hierarchy, though in a web namespace it appears to be just the opposite and the user might get confused. This can only be prevented by selecting reasonable object names.
Having made this decision a second problem arises. How do you involve PHP? The URL http://host/my_object will not call any PHP script unless you tell your web server to rewrite it to e.g. http://host/php_script/my_object and the script php_script evaluates the $PATH_INFO variable and retrieves the object with name my_object from the Hyperwave server. Their is just one little drawback which can be fixed easily. Rewriting any URL would not allow any access to other document on the web server. A PHP script for searching in the Hyperwave server would be impossible. Therefore you will need at least a second rewriting rule to exclude certain URLs like all e.g. starting with http://host/Hyperwave This is basically sharing of a namespace by the web and Hyperwave server.
Based on the above mechanism links are insert into documents.
It gets more complicated if PHP is not run as a server module or CGI script but as a standalone application e.g. to dump the content of the Hyperwave server on a CD-ROM. In such a case it makes sense to retain the Hyperwave hierarchy and map in onto the file system. This conflicts with the object names if they reflect its own hierarchy (e.g. by choosing names including '/'). Therefore '/' has to be replaced by another character, e.g. '_'.
Adding Hyperwave support to PHP should fill in the gap of a missing programming language for interface customisation. It implements all the messages as defined by the HG-CSP but also provides more powerful commands to e.g. retrieve complete documents.
Hyperwave has its own terminology to name certain pieces of information. This has widely been taken over and extended. Almost all functions operate on one of the following data types.
Several functions which return an array of object records do also return an associative array with statistical information about them. The array is the last element of the object record array. The statistical array contains the following entries:
The Hyperwave extension is best used when PHP is compiled as an Apache module. In such a case the underlying Hyperwave server can be hidden from users almost completely if Apache uses its rewriting engine. The following instructions will explain this.
Since PHP with Hyperwave support built into Apache is intended to replace the native Hyperwave solution based on Wavemaster, we will assume that the Apache server will only serve as a Hyperwave web interface for these examples. This is not necessary but it simplifies the configuration. The concept is quite simple. First of all you need a PHP script which evaluates the $_ENV['PATH_INFO'] variable and treats its value as the name of a Hyperwave object. Let's call this script 'Hyperwave'. The URL http://your.hostname/Hyperwave/name_of_object would than return the Hyperwave object with the name 'name_of_object'. Depending on the type of the object the script has to react accordingly. If it is a collection, it will probably return a list of children. If it is a document it will return the mime type and the content. A slight improvement can be achieved if the Apache rewriting engine is used. From the users point of view it would be more straight forward if the URL http://your.hostname/name_of_object would return the object. The rewriting rule is quite easy:
As an alternative to the Rewrite Engine, you can also consider using the Apache ErrorDocument directive, but be aware, that ErrorDocument redirected pages cannot receive POST data.
The behaviour of these functions is affected by settings in php.ini.
Table 1. Hyperwave configuration options
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
There are still some things to do: