helma.org

Differences between Helma 1 and Helma NG

It is quite obvious for anybody familiar with Helma 1 that NG is quite different in many fundamental ways. This article highligts some of the differences, and explains the reasoning behind these changes. I've grouped the changes into two groups: the big, obvious ones, and the smaller, not so visible ones.

Obvious Changes

More Javascript, Less Java

TODO

The Helma Shell

TODO

No HopObjects at the Core

TODO

Non-Obvious Changes

Non-accumulative Repository Chain

Like Helma 1, Helma NG is based on the concept of a list of repositories from which code and other resources are read. In fact, the repository package (contributed to Helma by Daniel Ruthardt) is one of the few larger packages of code Helma NG shares with its predecessor. However, Helma NG treats the repository path quite differently than Helma 1. Helma 1 in many cases treated the repository path in an accumulative way, meaning that things later on in the path could add to things defined in front of them. This was true for all kinds of properties files, scripts and skins. Helma NG, on the other hand, uses a more conservative approach: The first resource found in the repository path is used, and once the resource is found the search is terminated.

The reasoning behind this change is mostly to reduce complexity. Adding to one logical reource in several places can have terrible effects on clarity. By defining one thing in one place we hope to faciltate separation of concerns and improved molularity.

Jala Test NG port

Jala Test is (somewhat) functional on Helma NG! See attachments for screenshot, diffs and zip file. The changes are not that bad. I used the freshly committed helma.helma1 compatibilty module for this.

name	type	size
jalatest-ng.png	image/png	97683 bytes
jalatest.zip	application/x-zip-compressed	13987 bytes
jalatest.diff	text/plain	51321 bytes

To mount the test module's jala.test action in a Helma NG app as /test/jala.test do something like this:

  importModule('jala.test.*', 'test');

To mount the action as /jala.test do the following:

  importFromModule('jala.test.*', 'jala_test_action', 'jala_test_css_action');

Note that the path for the tests directory is currently hard-coded as /home/hannes/svn/helma-ng/modules/tests. You'll have to edit that path manually in the jala.Test.js file.

Type.properties Documentation

To store your HopObjects into a relational database system you need to define a database mapping. This is done in the type.properties files located in the persistent HopObject's prototype directory (e.g. apps/myApp/MyPrototype). The type.properties files contain no JDBC connection information, which is located in the db.properties file in the Helma installation directory.

Configuration Settings

 _db = datasourceName

The _db entry describes the database source to use for managing objects of this type. datasourcename is the connection's name defined in the db.properties, which is located in Helma’s installation directory or the application directory. The db.properties file contains information about the JDBC connections, like the JDBC driver, the connection URL and the database username and password.

 _table = tableName

The _table entry tells Helma which table to use for objects of this type within the database. To avoid problems with reserved words of SQL or your database system you should prefix your table names. (e.g. T_Story for the Story prototype’s table)

 _prototype

 _parent = localPropertyName, localProperty.parentsCollectionName, root.collectionName

The _parent entry contains a comma-separated list of properties of objects of this type to be used as parent. Objects must know their parent in order to generate correct URLs in their href() function. If a property in the list is null, Helma will look on the following one to fetch a parent object.

If an entry in the _parent item does not contain a dot, it is interpreted as an object property of the current object that acts as the object's parent. If an entry contains a dot character, the part after the dot is interpreted as a collection in the parent object in which the current object is contained. If the _parent is specified as "root", it is not interpreted as a property of the current object. Instead, the application's root object is used as parent object.

 _id = primaryKeyColumnName

The _id entry defines the column to use as primary key. Helma requires a single primary key with no other functionality.

 _children

Simple Attributes

 simpleAttributeName = tablecolumnname

Referenced Objects

 obj = object(SomeHopObject)

 obj.local

 obj.foreign

 obj.local.X

 obj.foreign.X

 obj.logicalOperator

Collections

 coll = collection(SomeHopObject)

 coll.local

 coll.foreign

 coll.loadmode

 coll.cachemode

 coll.order

 coll.filter

 coll.filter.additionalTables

 coll.hints

 coll.maxSize

 coll.accessname

 coll.group

 coll.group.order

 coll.group.prototype

Mountpoints

 moutpointName = mountpoint(SomeTransientHopObject)

Modules and Scopes in Helma NG

The javascript import features in Helma NG try to loosely imitate the semantics of python's import statement in order to allow applications to be written in a truly modular way. The magic of python's import statement is that a script never has to do anything special in order to avoid name clashes with other scripts, because every script lives in its one top level scope by default.

To sum it up:

You don't have to use any special Javascript syntax to denote a namespace. Every script is by its nature a separate scope, assigned to a namespace by the script that imported it.
It's virtually impossible to produce a name collision, as each script lives in its own scope.
Since scripts live in their own scope, imported scripts are only visible to the scripts that imported them.

Implementation

Helma NG implements this by using a separate top-level scope for each loaded script file, using a shared top-level scope as prototype. A simplistic implementation of most of the behaviour described above in the Rhino shell may look like this:

  // set reference to global object
  var __global__ = __global__ || this;
  
  function include(script, as) {
    var scope = new Object();
    scope.__parent__ = null;
    scope.__proto__ = __global__;
    // scope is now a top level scope that inherits 
    // from the global, shared top level scope
    scope.load(script);
    this[as] = scope;
  }

Of course, Helma NG also takes care of script reloading and stuff, and the shared module scope is really a per-thread scope that uses a really-shared scope for the really-shared stuff.

Example

Suppose there is a Javascript file called helma/database.js with the following content:

  function getConnection(...) {
      ....
  }
  
  function Connection(...) {
      ...
  }
  
  function Query(...) {
      ...
  }

Then consider the following statements in another script file:

importModule("helma.database")

This makes the functions defined in helma/database.js available in the current scope as

  helma.database.getConnection()
  helma.database.Connection()
  helma.database.Query()

importModule("helma.database", "db")

This makes the functions defined in helma/database.js available in the current scope as

  db.getConnection()
  db.Connection()
  db.Query()

importFromModule("helma.database", "getConnection", "Query")

This makes the functions defined in helma/database.js available in the current scope as

  getConnection()
  Query()

Note that the functions in helma/database.js do not care in which namespace they are loaded. They only see what is defined in their local file, and in the global scope shared by all modules. The scope that loaded the module is absolutely invisible to the loaded module! Also note that the getConnection() function in the last example can still access the Connection() constructor although it's not included in the importFromModule(). That's the power of closures!

Wiki Overview Text Draft

Most activity in the wiki currently revolves around working drafts for additional documentation and around Helma NG with a newly added dedicated Helma NG Wiki space.

Other important wiki pages are the lists of Related Projects and Sites using Helma, to both of which you are welcome to add your own or other missing entries.

Also helpful to find what you are looking for, may be the search page, the updates page, the tags cloud and the list of pages in the general wiki, which contains ideas, drafts and other miscellaneous bits and serves as an incubation space for new projects and documentation pages that may later be moved to their dedicated spaces.

Don't hesitate to just add a new page if you have something to contribute and are not sure where otherwise to put it.

Documentation Drafts

The current plan is to create a second wiki area specifically for the docs.

If you have ideas for how these documentation and training pages should be structured, the topics they should cover or if you can contribute something yourself, you may do so here in the wiki for brain storming purposes and proposals. Later we can move these bits to the new docs section.

Current working drafts in progress: (to propose a new draft, just add it to this list)

Helma Roadmap

Helma 1.6

Helma 1.6.2 is the current stable version of Helma and was released on April 7, 2008. You can get it from the download page.

See the Helma 1.6.0 Changelog, Helma 1.6.1 Changelog and Helma 1.6.2 Changelog for new features and bugfixes in Helma 1.6.

Helma 1.7

Helma 1.7.0 is planned for the middle of 2008 and will introduce significant new features to those found in Helma 1.6. See pages tagged with helma 1.7 for a list of planned features and the list of fixes and changes on track for Helma 1.7.

Helma 2.0

The roadmap for Helma 2 is being reassessed, since functionality that was intended for Helma 2 has now already been included in the Helma 1.6.0 release and development of Helma 1.x has been reenergized.

The implementation of Helma 2 has already been started, and is currently continuing under the code name "Helma NG", likely in parallel with the development of future Helma 1.x versions.

Collection Mapping

Naming conventions

All the tables and columns in the database are all lowercase. (Which is quite handy with an Mysql database because the names are case-sensitive if the underlying file system is also case-sensitive. So Mysql Names are case sensitive on Linux but not on Windows.)

Tablenames are plural.

Prototype names start with upper case and are camel case. Prototype names are singular.

Property- Object- and Collection-Mapping start with lower case and are also camel case.

Foreign keys are prefixed with the name of the table they are referring to.

1:n relation

DB schema

Mapping

Gallery/type.properties

   images         = Collection(Image)
   images.local   = gallery_id
   images.foreign = galleries_gallery_id

m:n relation

DB schema

Mapping

Image/type.properties

   tags                          = Collection(Tag)
   tags.filter                   = ${image_id} = tags2images.images_image_id AND \
                                   tags2images.tags_tag_id = tags.tag_id
   tags.filter.additionalTables  = tags2images

The Backslash "\" is only necessary when you have a filter that continues in the next line.

Object Reference Mapping (1:1 relation)

Naming conventions

Tablenames are plural.

Prototype names start with upper case and are camel case. Prototype names are singular.

Property- Object- and Collection-Mapping start with lower case and are also camel case.

Foreign keys are prefixed with the name of the table they are referring to.

DB schema

Mapping

Lets map the image_data to our image!

Image/type.properties

   imageData          = Object(ImageData)
   imageData.local    = image_id
   imageData.foreign  = images_image_id

This code is in the type.properties file of our Image prototype. We specify which prototype should be mapped with the Object() instruction. You have to specify the name of the prototype here. To the properties.local and .foreign you must assign the names of database columns.

Sites using Helma

Some example sites built using Helma:

247street.net - weblog community
alphazoo.at - weblog community
antville.org - weblog community
appjet.com - in-browser IDE for building and hosting web apps with javascript
blogger.de - weblog community
blogmax.at - weblog community
blogr.com - your space for photos, videos, podcasts and your blog
blogs.macbay.de - weblog community
blogs.uni-erlangen.de - university weblogs
blogverzeichnis.krone.at - weblog directory
club3k.at - webchat community and social media site
collabor.f4.fhtw-berlin.de - education weblog community
derwesten.de - media and community site
dubistnews.at - weblog community
evolver.at - webzine
fm4.orf.at - public broadcast media site
fritz.salzburg.com - entertainment community site
futurezone.orf.at - public broadcast media site
hausverein.ch - corporate/association site
hektor.ch - project site for Hektor, the spray-paint output device
helma.org - project site, wiki, blog
henso.com - personal site, blog
ideenbüro.org - corporate site, wiki, blog
knallgrau.at - corporate site
kontakt.erstebankgroup.net - corporate site
kontakt-collection.net - corporate site
lineto.com - corporate site and web shop for original digital typefaces
meinekleine.at - media community site
mumundo.net - project site
mywoman.at - weblog community
myworld.bluewin.ch - weblog community and social media site
oe3.orf.at - public broadcast media site
oesterreich.orf.at - public broadcast media site
p3k.org - personal site/blog
parq.at - corporate site
iphone.boozle.de - ORF.at for iPhone
plastikmaedchen.net - personal site
politikblogs.at - weblog directory
polylog.tv - social media site
preachingtheword.net - audio sermon archive
radiograz.at - media and community site
shnitzl.org - add, share, organize and discover great events
science.orf.at - public broadcast media site
scratchdisk.com personal portfolio site
scriptographer.com - project site for a JavaScript scripting plugin for Adobe Illustrator
shapeshifters.net - community site for creatives
sosmitmensch.at - human rights pressure group
spinnenwerk.de - weblog community
tonight.rp-online.de - party portal and community
twoday.net - weblog community
twoday.tuwien.ac.at - university weblogs
typolis.net - weblog community
tz-online.de - media and community site
vistablog.at - corporate blog
Webmark - Managementinformationssystem
weblife.at - community and social media site
weblogs.brandnews.at - weblog community
westropolis.de - culture community site
zumbrunn.com - corporate/personal site

Organizations with projects based on Helma:

Alliance for Nonprofit Management, Washington DC
AOL, New York
Bauhaus-University of Weimar, Germany
BauMax, Austria
Berliner Jugendserver Spinnenwerk, Germany
Brandenburg University of Applied Sciences, Germany
Canton of Berne, Switzerland
Casa Consult, Switzerland
Chris Zumbrunn Ventures, Switzerland
collettiva design, Austria
Dr. Sauer Group, Washington DC
Electricité Plainpalais, Switzerland
Green Party Berne, Switzerland
FHTW University for Applied Sciences Berlin, Germany
Forum for Direct Democracy, Switzerland
Harvard University, Center for Hellenic Studies, Washington DC
Hausverein Schweiz, Switzerland
Ideenbüro, Switzerland
IQ-plus Medien, Austria
K12, Virginia
Kleine Zeitung, Austria
Knallgrau New Media Solutions, Austria
Lakeland Catholic Schools, Alberta, Canada
Lineto, Switzerland
MANOVA NetBusiness Solutions GmbH, Austria
Microsoft, Austria
Munich Online, Germany
NAFSA Association of International Educators, Washington DC
National Gallery of Victoria, Australia
National Geographic, Iowa
Netural Communication, Austria
Nuclear Energy Institute, Washington DC
ORF, Austria
Parq, Austria
Rheinische Post Online, Germany
Ringier, Switzerland
Rundfunk Berlin-Brandenburg, Germany
Salzburger Nachrichten, Austria
Shapeshifters information management, Austria
Siteworx, Virginia
SOS Mitmensch, Austria
Sumaato, Ubilabs, Germany
Swiss Army, AFD, Switzerland
Swiss Red Cross, Switzerland
Swisscom, Switzerland
Swisspost, Switzerland
SysEleven, Germany
System One, Austria
Technical University of Vienna, Austria
Telecom Austria, Austria
Unilever, Austria
United Press International, Washington DC
University College of Falmouth, United Kingdom
University of Berne, Switzerland
University of Erlangen, Germany
University of Vienna, Austria
Verlagsgruppe NEWS, Austria
WAZ NewMedia, Germany
ZLB Bioplasma, Switzerland