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Subject: Re: [xdi] proposal for binary data literal node

The order of statements should never impact anything at all.
The server should read the entire message and then process it.
(BTW I don't think we have ever specified in which format a client sends messages to the server).

So I still don't understand why the server can't just look at the data and metadata at the same time.
Shouldn't everything be available by the time the server starts processing the message?


On Fri, Mar 2, 2012 at 4:42 PM, Michael Schwartz <mike@gluu.org> wrote:

I don't care about !!, it is just a starting point :)

You can't specify what order the client sends the XDI statements, so you can't "specify the metadata always be loaded first"

If we specify that binaries are encoded in a certain way using the data URI format, that might be a solution because in one XDI statement, we can determine that we are dealing with a binary.

- Mike

On Fri, 2 Mar 2012, Barnhill, William [USA] wrote:

To make this work I think we need to first specify how a binary would be serialized in the XDI serialization protocol. Since that is based on JSON you either must use an encoding (i.e. data URL, or MIME), or have some part of multi-part message with the binary as a different MIME type.  I think we need to specify how to handle binaries, but I don't think !! is the answer.  I think specifying that the metadata always be loaded before the value or a literal is processed, may be the answer, which would allow our existing mechanisms for specifying the binary MIME type (we still don't have serialization finalized, currently encoding is used I believe by several of us).

Kind regards,
Bill Barnhill
Booz Allen Hamilton - Belcamp,MD
1-443-924-0824| barnhill_william@bah.com

-----Original Message-----
From: xdi@lists.oasis-open.org [mailto:xdi@lists.oasis-open.org] On Behalf Of Michael Schwartz
Sent: Friday, March 02, 2012 10:24 AM
Subject: Re: [xdi] proposal for binary data literal node

I want to stress that storage of binaries is not a niche use case. It doesn't matter what kind of implementation you are using--rdbms, ldap, or file system--you will want to treat binaries differently. An implementation detail is what do you do with the binaries, not whether you know if you have a binary.

If we don't solve this, and we're stuck with some lame solutions like encoding binaries (i.e. like in SMTP), it would be a missed opportunity for the TC.

How about a new type of arc: the "binary arc" ?

See inline comments below.

If for optimization purposes a server needs to know the data type of a
literal (binary, number, boolean, etc.), then it could either 1.
figure out the data type based on the dictionary, or

I don't understand your suggestion here. How would a dictionary be helpful? How could you guarantee that the dictionary is known when you are parsing the XDI statements?

2. require (as a policy) that clients add the literal together with
the metadata that specifies the data type

no, per my previous comment, there is no guarantee the metadata would be loaded first.


On Fri, Mar 2, 2012 at 3:05 PM, Michael Schwartz <mike@gluu.org> wrote:

I think we need a way to differentiate binary literals if we want to
support storage of binaries in the graph. And simply storing metadata
is not sufficient because there is no guarantee that the metadata is
created before the literal needs to be stored. Is there a solution?




Michael Schwartz
Founder / CEO
+1 646-810-8761

On Thu, 1 Mar 2012, Drummond Reed wrote:

 Mike, the question you raised actually highlights a number of the
reasons for the literal context proposal. Let me explain.

First, per Markus' last point in his message, one primary purpose of
literal contexts is so an XDI processor always knows the type of the
literal node it is dealing with by the type of the literal context.
To use Mike's example, if "*logo" is defined as a literal context
containing a binary value (which has several semantic issues -- see
below), then @!1111*logo always identifies a single binary value.

Secondly, it's a misunderstanding of literal contexts that there
could be two literal arcs. The whole idea of a literal context is
that it has a single literal arc. If the literal context is defined
as containing binary data, then that literal arc points to binary
data. If the literal context is defined as containing a number, then
the literal arc points to a number.
And so on.

These are all controlled by XDI dictionary definitions, which is why
I think the XDI Dictionary spec is moving up in priority.

Now, the semantic issues. First, @!1111*logo is semantically wrong
because uses a *name to identify a literal context defined in a
dictionary, and * is not the dictionary namespace. The dictionary
namespace is + (with the exceptions of a handful of special $words defined by the XDI TC).

So it should be @!1111+logo. The second semantic issue is that +logo
should not be a literal context because it is not a single defined
should be a supertype that has defined subtypes. In other words, the
dictionary defintion should say +logo/$is$a/+image, and (among other
options) +$image/$a/$a$xsd$jpeg. So if the binary you wanted was a
JPEG, then the address would be:

 1. @!1111+logo$a$xsd$jpeg  <== canonical JPEG version of the logo
 2. @!1111+logo/$a$xsd$jpeg  <== (note the slash) relational arc

 to all the JPEF versions of the logo (zero-or-more)

So it is the dictionary-defined  $jpeg, and not +logo (and
definitely not
*logo) that is the XRI literal context storing the binary data. And
because the $dictionary will define $jpeg as a JPEG binary, any time
an XDI processor sees $jpeg as the literal context, it knows the
value is a JPEG.

I'll put this on the agenda for tomorrow's call (even though Mike
won't be there).

On Thu, Mar 1, 2012 at 4:35 PM, Michael Schwartz <mike@gluu.org> wrote:


Thanks for the quick response!

1. Yes, you could have both a ! and !! arc, why not?  It doesn't
seem inherently problematic to me.

2. yes, you're right I forgot the / for the literal arc :)

3. !! was just an idea... it could be something else.

4. Its useful to be able to differentiate binary data from other
types of  data because there persistence strategy varies greatly.

- Mike

 1. Could you have BOTH a binary and a non-binary literal in a context?

have a ! arc and a !! arc.
If not, will the server throw an error if you already have one
literal and try to add the other one?

2. In your example, wouldn't the XRI actually be @!1111*logo/!!
instead of @!1111*logo!!  ?

3. Something is bothering me about the fact that !! is two subsegments.
am worried it will result in ambiguity in one way or the other.

4. I don't understand why you can't load the metadata together
with the literal, to figure out whether it is binary or not.
Wasn't this the whole point of what Drummond called "literal contexts"?


On Thu, Mar 1, 2012 at 9:49 PM, Michael Schwartz <mike@gluu.org> wrote:


I'm attaching a proposal to represent binary literal values as "!!"

So, for example, the XRI for a my company's logo might be :

The fact that the image is a binary can't be represented in the
metadata, because it is not known which will be loaded first, the
literal node, or the metadata about the literal node.

This is a critical issue to optimize persistence of binary
objects, which need to be indexed differently.

I'd like to fast track this because we need to store binaries as
part of the oxPlus demo :)



- Mike

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