I prefer use of xs:anyUri, it gives a clear indication that this a reference to the data and not the data itself. I prefer dfdl:objectKind - the object is not necessarily large, the author might want a reference for other reasons. Regards Steve Hanson IBM Hybrid Integration, Hursley, UK Architect, IBM DFDL Co-Chair, OGF DFDL Working Group smh@uk.ibm.com tel:+44-1962-815848 mob:+44-7717-378890 Note: I work Tuesday to Friday From: "Lawrence, Stephen" <slawrence@tresys.com> To: "mbeckerle.dfdl@gmail.com" <mbeckerle.dfdl@gmail.com> Cc: "dfdl-wg@ogf.org" <dfdl-wg@ogf.org> Date: 12/08/2019 12:16 Subject: Re: [DFDL-WG] BLOB - binary large object proposal - updated Sent by: "dfdl-wg" <dfdl-wg-bounces@ogf.org> dfdl:largeObjectKind definitely keeps things simple, but does lose flexibility (e.g. maxLength). But that may not be needed. I'm in favor of this. However, one drawback of using xs:string instead of xs:anyURI relates to our TDML test rig. If we make the type of blobs/clobs an xs:string and have it be an opaque identifier then it makes it difficult for our TDML runner to know how to compare actual vs expected blobs. For example: <data xsi:type="xs:string">some unique identifier</data> In this case, the TDML test rig must be schema aware to know that data is not a string and is actually an opaque identifier. And it must know how to use that unique identifier to lookup the bytes to do expected/actual comparisons. By making the type an xs:anyURI and requiring that the identifier is a URI, a TDML runner does not need any knowledge of the schema. Since the xsi:type is an anyURI, it can infer that this must be a blob/clob, and then it can open the URI to determine the bytes and easly compare expected vs actual blobs. And this applies to anyone accessing the infoset as well--not just our TDML runner. Using a type of xs:anyURI provides a hint to infoset users that an element shouldn't be treated like a string, but as a blob handle. - Steve On 8/9/19 10:25 AM, Mike Beckerle wrote:
My suggestions based on this thread are:
I think the dfdlx:blob type is problematic, and we should avoid it in
xs:string with a dfdlx:largeObjectKind property.
I think this should not be a "Type" as in string or hexBinary, because hexBinary is such a misleading term, suggesting textualization, etc. There is nothing "hex" about a BLOB, ever.
I think dfdlx:largeObjectKind="bytes/chars/none" with none the "default" for now, and "chars" as a future capability for character large objects if
prove important. I could be convinced other enums are better than bytes or chars for
BLOB, CLOB might be better. Or perhaps this is dfdl:largeObjectRep="binary/text/none" analogous to the dfdl:representation property?
The use of xs:anyURI is unnecessary, and is not a type we have in DFDL as yet. People should treat this string as opaque. The fact that it is
meaningful URI is not relevant, and can be an implementation detail.
I think dfdl:largeObjectDirectory="{ $dfdlx:largeObjectDirectory }" is a nice idea to save for the future. We may find that numerous other parameters are required, so I'd prefer not to predefine this one in advance of clearer direction or whether there are others.
The other thing observed on yesterday's DFDL WG call, was that this has some overlap with the offset/pointer stuff. Unparsing from a blob file is an awful lot like data-source indirection where the source of unparsing is coming from a scattered data structure that is being gathered. There is some conceptual similarity anyway. Not sure how deep this goes or if it is just a superficial observation. And I would not suggest waiting for that to be figured out before proceeding with this experimental BLOB feature.
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com < https://urldefense.proofpoint.com/v2/url?u=http-3A__www.tresys.com&d=DwICAg&c=jf_iaSHvJObTbx-siA1ZOg&r=AJa9ThEymJXYnOqu84mJuw&m=RHrC943K_Ebv1XG4NHnze7AdBgWDS_Vfjb_pYsDIQ5U&s=yyn8_2c8iwgOiiXgq-ZPoPKMKJo7FKAgHWXNYR-PQ3w&e=
Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy < https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ogf.org_About_abt-5Fpolicies.php&d=DwICAg&c=jf_iaSHvJObTbx-siA1ZOg&r=AJa9ThEymJXYnOqu84mJuw&m=RHrC943K_Ebv1XG4NHnze7AdBgWDS_Vfjb_pYsDIQ5U&s=rDxL7k1L1pv9xIdXwaEB_8Pa9Twy8dwgsicarX3l6QQ&e=
On Thu, Aug 8, 2019 at 8:40 AM Lawrence, Stephen <slawrence@tresys.com <mailto:slawrence@tresys.com>> wrote:
The intention was that this new type would be an internal built-in type and so no extra properties could be placed on the new simple type. One drawback that I'm realizing as I implement this feature in Daffodil, is that in order to use non DFDL aware XML Validation tools to validate
favor of a they this. Eg., potentially a the
XML infoset, you need to provide and xs:import this new DFDL schema
that
defines the dfdlx:blob type, which feels a little awkward to me for something that's considered a built-in for DFDL processors.
Maybe an alternative would be to not have a dfdlx:blob type, allow
the
use of the xs:anyURI type for simple elements, with the implication
that
we treat the element as if it were xs:hexBinary except for the infoset/blob output. This doesn't easily support CLOB's, but a new
DFDL
property could determine how an xs:anyURI should be interpreted,
e.g.:
<xs:element name="myBlobData" type="xs:anyURI" dfdl:largeObjectType="xs:hexBinary" ... />
<xs:element name="myClobData" type="xs:anyURI" dfdl:largeOjectType="xs:string" ... />
So a type of xs:anyURI implies this is going to be some kind of
large
object representation, and it requires the dfdl:largeOjectType
property
that must reference a simple type that defines how the content
should be
turned into an large object. This might also help to support restrictions on the blob data, as well as implicit lengths, e.g.:
<xs:simpleType name="blob10"> <xs:restriction base="xs:hexBinary"> <xs:maxLength value="20" / </xs:restriction> </xs:simpleType>
<xs:element name="data" type="xs:anyURI" dfdl:objectType="blob10" dfdl:lengthKind="implict" />
DFDL properties could be placed on either the element or the
objectType
simpleType, with the base type of dfdl:largeObjectType determining
which
properties are valid/interpreted, rather than the element type
(which
must be anyURI).
But maybe this all adds unnecessary complexity?
Regarding specifying the filename via a DFDL property rather than
API,
we have a use cases where each parse would need to output to a
different
directory so a property might cause problems with this. But perhaps
this
could be handled by a variable, e.g.:
<xs:element name="data" type="dfdlx:blob" dfdl:blobDirectory="{ $blobDir }" ... />
That said, we had additional use cases where a DFDL blobDirectory property would be too restrictive. For example, maybe the blobs
should
be put into a database, or pushed to a data store in the cloud,
stored
in local memory, or not stored anywhere at all but with a special
URI
with offset+length to the original data. We chose to ignore these use-cases for simplicity, but these different options would probably require a flexible API to support. By going with an API to specify
the
output directory, it makes it a bit easier to support these
different
blob outputs in the future if it was needed.
On 8/8/19 5:09 AM, Steve Hanson wrote: > Mike > > Am I allowed to put DFDL properties on the new simple type, or is
the new
type > considered to be a built-in type? I think the latter is clearer
and
simpler to > implement. Support for 'clob' would then just add a new simple
type
restriction > 'dfdlx:clob'. > > Assuming that the feature makes it into a future DFDL 2.0, the
schema
containing > the 'blob' simple type would then be in the standard DFDL
namespace.
That's the > first example of such a schema, as this is the first time we are extending base > XML Schema as opposed to defining annotations. If the new type is considered a > built-in type, then this schema should be part of the DFDL 2.0
standard and
> read-only. > > Any thoughts on allowing the specification of the filename via
DFDL property
> rather than API call? > > Presumably I could create a local restriction of 'dfdlx:blob'?
One
motivation > for so doing would be to validate the length or content of my
binary data.
> There's a problem with that though - validation works against the infoset, so > the allowable facets are those applicable to xs:anyUri and would
be
applied to > the file name, not the binary data. It also means that
dfdl:lengthKind
> 'implicit' can't be used. I don't see a way round this. > > Regards > > Steve Hanson > > IBM Hybrid Integration, Hursley, UK > Architect, _IBM DFDL_ <http://www.ibm.com/developerworks/library/se-dfdl/index.html> > Co-Chair, _OGF DFDL Working Group_ <
_ > __smh@uk.ibm.com_ <mailto:smh@uk.ibm.com <mailto:smh@uk.ibm.com>> > tel:+44-1962-815848 > mob:+44-7717-378890 > Note: I work Tuesday to Friday > > > > From: Mike Beckerle <mbeckerle.dfdl@gmail.com <mailto:mbeckerle.dfdl@gmail.com>> > To: DFDL-WG <dfdl-wg@ogf.org <mailto:dfdl-wg@ogf.org>> > Date: 12/07/2019 18:14 > Subject: [DFDL-WG] BLOB - binary large object proposal - updated > Sent by: "dfdl-wg" <dfdl-wg-bounces@ogf.org < mailto:dfdl-wg-bounces@ogf.org>> > >
--------------------------------------------------------------------------------
> > > > This concept, ,which has been discussed before, is in high demand
in the
> Daffodil user community to enable DFDL to be used to parse image
file
formats. > The use case is to provide uniform image-metadata access without
getting
bogged > down in the large byte-array that makes up most of the file and
would be
very > large (and pointless) if rendered into XML or JSON. > > So our proposal, (which will get turned into an official
Experimental
feature > document), has been simplified and revised and is described here: > >
> > > Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | > _www.tresys.com_ <
> Please note: Contributions to the DFDL Workgroup's email
discussions are
subject > to the _OGF Intellectual Property Policy_ > <
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