[CompStrm Wiki] data proxies

[Bill la F. <laf...@ya...>]

Everyone,

Here's a quick note on data proxies (below). Please
let me know if this helps or not! Any feedback you
have would be appreciated.

Bill

AgileWiki3 uses proxies for accessing data, the proxy
object holding only the rid (rolon identifier), a 128
bit random number.

But these are data proxies. The database holds only
the data. These proxy objects implement the methods.
Is this  a break from object oriented programming? No
more than object serialization where the pickled
object identifies the class type. The difference here
is that the data is not put in the proxy object.
Rather it is cached. This gives us a big speed
improvement. It also makes it easier to manage
inverted data (indexes).

By convention (not a requirement), the data proxy
classes are in package org.agilewiki.ark.rolons. The
base class is Rolon, and its a bit big.

There is a descriptor entry, Type, which identifies
the class of data proxy to be used. And in package
org.agilewiki you will find a resource file,
rolons.txt, which maps type names to data proxy class.
Currently this table has 12 entries.

Now every rolon has a descriptor unit rolon (a du)
which also defines a kind of type, but this is a finer
grained mapping--you can have multiple descriptor
units which work with the same type of rolon.

Every descriptor unit has a ledger entry, Type, which
identifies the type of rolon that the descriptor unit
works with. This is used when creating new rolons--you
identify the descriptor unit to be used and use the
DU's Type LEnt to determine the Type DEnt of the rolon
being created.

There are then only 3 steps to extending the object
model:

1. Write a new data proxy class which extends
org.agilewiki.ark.rolons.Rolon. This class must
include, among other things, a static narrowing
method.

2. Add a line to the rolons.txt file which gives the
name of the new type of rolon and its class.

3. Create a DescriptorUnit rolon with a Type LEnt that
names the new rolon type.



		
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