[LC-1971] RE: DDR Simple API

Hello José,

 

Thank you for your comment. We have recorded this as 'LC-1971' and will reply to you as soon as possible. Please use the code LC-1971 in future correspondence regarding these comments.

 

On behalf of DDWG,

Rotan Hanrahan,

Chair.

 

From: public-ddwg-comments-request@w3.org [mailto:public-ddwg-comments-request@w3.org] On Behalf Of Jose Alberto Fernandez
Sent: 15 April 2008 15:52
To: public-ddwg-comments@w3.org
Subject: DDR Simple API

 

Hi,

 

I have been having some discussions with other members of the wmlprogramming mailing list and after taking a look at the current draft of the "Device Description Repository Simple API" I have found at least on minor issue with the API as currently defined.

 

For what I have read, the API is lacking mechanisms to discover the types and values of Properties. To make myself clear, on 4.2.4 it states: "For the getString method implementations must return an implementation dependent String representation if the type of the value is not natively String." There are two readings to this sentence: (a) Strings will be represented on the native string representation for the specific language of the implementation; this sounds completely fine. But another reading (b) would be that the string representation of the values is dependant on each implementation; now this would mean one implementation may "display" integer values as binary while another as decimal or hexadecimal. One implementation may represent Boolean values as "0"/"1" another as "false"/"true" or "no/yes". This of course would diminish the usability of PropertyValue.getString() as a way to fetch values in a universal manner.

 

This would be acceptable if there were a way to discover the type of Properties. But there is none. 4.2.4.1 provides a mechanism to discover if a Property exists, but no mechanism to interrogate what is the type and hence what Retrieval method to use. It seems to me a way to discover the type of a PropertyValue is needed either directly on PropertyValue or as an attribute of PropertyRef:

 

             int getPropertyType() : One of constants: LONG_VALUE, DOUBLE_VALUE, STRING_VALUE, BOOL_VALUE, INT_VALUE, ENUMERATION_VALUE, FLOAT_VALUE.

 

I am suggesting int constants to keep the API simple and compatible across languages; as oppose to returning a instance of a Java Enum or Class.

 

Notice that the DDR implementation itself has to know the type as otherwise it would not be able to throw the expected exception in case of error. But without this functionality at the API level there is no way for programs using the API to do any kind of discovery.

 

Hopping you take my comments into concideration.

 

Regards,

 

Jose Alberto Fernandez

Cellectivity LTD