SIXX - Smalltalk Instance eXchange in XML

Description

SIXX is an XML serializer/deserializer written in Smalltalk (currently Squeak 3.2, VisualWorks 5i.4 - 7, Dolphin XP and Smalltalk/X are supported). The purpose is to store and load Smalltalk objects in a portable, dialect-independent XML format, providing a functionality simular to storeOn:, storeBinaryOn: and storeXMLOn: (sigh - yet another format).

Design Policies:

Simple:

SIXX format is human and machine readable. It basically uses only one XML element tag. (Please see SIXX instance example and SIXX schema).

Portable:

SIXX implementation is carefully written so that it only uses portable Smalltalk methods. ( It avoids using dialect-specific methods). Furthermore, SIXX is not particular about XML parsers. DTD validation nor namespaces support are NOT needed to implement SIXX. The present implementation (for Squeak) has already been working both on YAXO and VWXML.

Smart:

SIXX resolves shared/circular object references. Unlike classic #storeOn: and #readFrom:, it never create copies. Advanced users can implement custom serialization/deserialization format by overriding only a few hook methods.

Implementation:

Currently, the implementation is provided for Squeak 3.4, VisualWorks 5i.4-7, Dolphin XP and Smalltalk/X. (Sorry for other dialect fans, please see the future plan.)

Prerequisites:

XML Parser:

Squeak:

Two XML parsers (YAXO and VWXML) are supported.

• YAXO which is included in Squeak 3.4
• or VW XML Parser ported by Bijan Parsia

VisualWorks:

Sixx runs on the default VW XML parser (VWXML).

Dolphin:

Sixx runs on YAXO for Dolphin, ported by Steve Waring.

Smalltalk/X:

Like with Squeak: Sixx can use YAXO or the VW XML Parser.

Installation:

Squeak:

Extract the zip file to your Squeak root directory and just file in 'install.st'.

VisualWorks:

Extract the zip file to any parcel directory and parcel in 'SIXX-Install'.

Dolphin:

Extract the zip file to your Dolphin root directory and install a package named 'SIXX Install.pac'.

Smalltalk/X:

Sixx is already installed as a bunch of autoloaded classes.

Limitations:

• SIXX cannot store/load context objects.
  as a consequence, full blocks (which refer to home-context variables) can also not be represented in sixx.

Download:

Current releases and snapshot:

Squeak:

• SIXX ver0.1g all (2003/6/12)
• SIXX ver0.1g sar (2003/6/12) - for Squeak 3.4-3.5 users
  • sixx-patchNihongo20030318.cs - a patch for SqueakNihongo4

VisualWorks:

• SIXX-VW ver0.1g (2003/6/12)
  • Also available in Cincom Public Store Repository

Dolphin:

• SIXX-Dolphin ver0.1g (2003/6/12)

Smalltalk/X:

• Sixx is already included in the base system.

For porters:

• SIXX in SIF (2003/6/12)

For formalists:

• SIXX DTD: (2003/03/25) - This is not important for just using SIXX. I wrote it for advanced developers who are curious about SIXX elements and attributes semantics.

License:

• SIXX is under original license (MIT, XFree86 style), intended to be easily linked to Squeak image file.

No Warranty

How to use (Examples):

Basic writing/reading:

SIXX is very easy to use. Like #storeString, You can generate a SIXX string by #sixxString.

    array := Array with: 1 with: 'Hello' with: Date today.
    array sixxString.

This code generates a SIXX string below:

'<sixx.object sixx.id="0" sixx.type="Array" >
    <sixx.object sixx.id="1" sixx.type="SmallInteger" >1</sixx.object>

    <sixx.object sixx.id="2" sixx.type="String" >Hello</sixx.object>
    <sixx.object sixx.id="3" sixx.type="Date" >16 June 2002</sixx.object>

</sixx.object>
'

This string can be read by #readSixxFrom:.

Object readSixxFrom: sixxString. "sixxString is the above string"

Stream writing/reading:

SixxWriteStream and SixxReadStream are provided so that you can write/read Smalltalk objects like a binary-object-stream way. (Yes, the BOSS in VW, and the ReferenceStream in Squeak).

In order to write objects to an external file, you can:

    sws := SixxWriteStream newFileNamed: 'obj.sixx'.
    sws nextPut: <object>.
    sws nextPutAll: <collection of object>.
    sws close.

And to read objects from an external file:

    srs := SixxReadStream readOnlyFileNamed: 'obj.sixx'.
    objects := srs contents.
    srs close.

Future Plan:

(2002/09/15)

• Porting to other Smalltalks (VisualAge Smalltalk, SmallScript, etc). Contributors are welcome!

Related Links:

Other XML object serializer/deserializers:

There are XML object serializer/deserializers already available. (Generally speaking, SIXX is much simpler, because it has been specialized for Smalltalk.)

For ODMG objects:

• OIFML - Using XML as an Object Interchange Format (ODMG)

For Java objects:

• Castor (ExoLab Group)
• JROM (IBM alphaWorks)

SMIX (SMalltalk Interchange Format in XML):

SIXX is designed for serializing/deserializing object instances "data"(states). If you would like to save/load Smalltalk class definitions, use SMIX, instead.

Suggestions?

Authors are:

• Masashi Umezawa (Squeak, VW, Dolphin)
• Tetsuya Kurihara (Squeak)
• Kazuki MINAMITANI (VW, Dolphin)