[kepler-dev] [Ptango] Re: ObjectToRecord related questions

[Christopher Brooks]

Beth Latronico asked me to forward on the following about this issue.

Beth writes:
>
> We ran into a similar problem trying to build an actor which reads 
> information in JSON from a web page and outputs a RecordToken.  Here’s 
> a summary of the discussion and a sample model in case this is helpful 
> for your situation!
>
> Actor:  ptolemy.actor.lib.conversions.JSONToRecord
>
> Test model:  ptolemy.actor.lib.conversions.test.auto.JSONToRecord1.xml
>
> Ideally we wanted to be able to set the type of the output to a 
> RecordType including all of the fields and types of those fields (vs. 
> an empty Record), so that we could use the RecordDisassembler.  
> However, since the type solver only runs once and runs during 
> preinitialize(), this means we need to get the type information 
> somehow ahead of time, and that the type signature cannot change 
> during execution.  (It’s OK if the data changes).
>
> For some web data streams, this seems OK – the type signature is 
> always the same – so we pull some sample data in preinitialize() to 
> determine the type, and then check the type signature in fire() to 
> make sure it has not changed.  This assumes that we know the URL of 
> the data source, the URL remains fixed and that sample data is 
> available before the model executes.
>
> For other web data streams, the type signature changes.  Here we 
> currently set the output port type to an empty record so at least the 
> type solver knows it’s a record, but then we can’t connect this output 
> to a RecordDisassembler – it would throw an exception when the model 
> is executed.
>
> Token value = new RecordToken();
>
> output.setTypeEquals(value.getType());
>
> So, we’re debating on whether 1) these two cases should be split into 
> different actors, and 2) if it’s appropriate to use RecordDisassembler 
> or should we create some new actors that can handle loosely-typed records.
>
> Also like you mentioned for objects, JSON is fairly close to a Ptolemy 
> record, but like Java types, the JSON types are not exactly the same 
> as Ptolemy types.  (For example, it looks possible that JSON arrays 
> could contain mixed types in the same array).  We don’t have a good 
> solution for that yet…  right now we are just extracting Ptolemy types 
> and hoping for the best.
>
> Unfortunately there are more questions than answers at the moment, but 
> hope the discussion highlights some of the issues!
>
> Best,
>
> Beth
Marten Lohstroh suggested that we could have a flag that when set 
required strict typing.  Certain actors could record the type 
information in a manner similar to how the Test actor works.  The Test 
actor has a shared parameter called "trainingMode".  When trainingMode 
is true, the known good results of the TestActor is recorded.  In a 
similar manner, certain actors could record the type information when 
trainingMode was set to true.


_Christopher

On 4/2/12 6:05 PM, Edward A. Lee wrote:
>
> Ptolemy II is statically typed, so after a model is preinitialized,
> the types of all ports must be known. The type system is described in
> chapter 5 of this document:
>
> http://www.eecs.berkeley.edu/Pubs/TechRpts/2008/EECS-2008-29.html
>
> and also in this paper:
>
> http://chess.eecs.berkeley.edu/pubs/665.html
>
> For Record types, the most general record type is the empty record type.
> That is, a record type {fieldName = double}, for example, is also
> an instance of {}, the empty record type. Moreover, a record of
> type {a = int, b = double} is also an instance of {a = int}.
>
> So, for example, if you know that your output record will contain
> a field named "a" of type "int", then you can force the output type
> to be {a = int} (right click on the actor, select Configure Ports,
> and enter "{a = int}" in the type field). As long as there is actually
> such a field, in the record, this will work. But if you run the model
> and there is no such field, I believe you will get a run-time type
> error (which is probably what you want).
>
> Edward
>
>
> On 4/2/12 1:51 PM, Hogan, D. (GE Energy) wrote:
>> I have an actor that uses the structure of a file generated at runtime
>> to create an output record.  The actor is working, but I have a few
>> questions on ObjectToRecord since it is similar.
>>
>> In ObjectToRecord, it does not change the type and lists it as fixme.
>> The documentation for RecordType mentions using setTypeAtMost(new
>> RecordType(new String[0], new Type[0])) when you want to specify a
>> record without specifying the fields.  Should I use that?  Is there a
>> better way to specify it is a record and the field names/types are
>> discovered at runtime?  Since unknown matches that type constraint, what
>> is the best way to handle this?
>>
>> ObjectToRecord doesn't try to convert between standard Java types and
>> Ptolemy types.  I noticed there is a
>> ptolemy.data.expr.ConversionUtilities, but it looks limited to the
>> expression language needs.  Is there another conversion in Kepler?
>>
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-- 
Christopher Brooks, PMP                       University of California
CHESS Executive Director                      US Mail: 337 Cory Hall
Programmer/Analyst CHESS/Ptolemy/Trust        Berkeley, CA 94720-1774
ph: 510.643.9841                                (Office: 545Q Cory)
home: (F-Tu) 707.665.0131 cell: 707.332.0670

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