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What does "persist" really mean ?

 
 
Tom Anderson
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      08-01-2008
On Thu, 31 Jul 2008, Lew wrote:

> Lew wrote:
>>> XML has many benefits as an serialization format, not least that it is
>>> semantically void.

>
> Tom Anderson wrote:
>> "Semantically void"?

>
> XML formats do not depend on nor impinge on the meaning of the content.
> Put another way, XML (like ASN.1 from what you've told us) is
> self-describing, so one need not refer to an external source to
> interpret the contents.


Right, got it.

> The meaning is entirely at the endpoints of an XML document's use, not
> internal to the document. With other formats, for example positional
> layouts where a field belongs to a certain position on a line, the
> semantics are part of the format.


Yes. XML is more of a format architecture than a format per se, and it's
the formats you define with XML that impose meaning.

Although one could argue that XML does impose some meaning, in that it's
hierarchical: it doesn't have a natural way to describe directed acyclic
graphs, or matrices. The ID/IDREF mechanism does give you quite a good way
to do DAGs, but it's not quite as natural as the way XML deals with
hierarchies.

tom

--
Faith in chaos.
 
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Arne Vajh°j
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      08-02-2008
SÚbastien de Mapias wrote:
>> In the case of Spring/Hibernate I bet in 99% of cases it means it will
>> issue an SQL insert or update statement to a nearby DBMS.

>
> OK in this case 'save()' does not really "persist" the object *yet*,
> until I commit, isn't it ?


Now you really need a precise definition of persist.

Save will send the data to the database. And it may be seen
by other processes if the transaction isolation level is low.
But until commit is called then the data can still be told to
go away.

I will tend to agree with you: data is first persisted when they are
committed.

Arne


 
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