Ah, yep that makes perfect sense. Thank you Steve.
What is the lesson learned?
Earlier I learned this lesson with regexes: in a list of alternatives, list the
longest alternative first, e.g., foobar|foo not foo|foobar
Is that lesson rearing its ugly head again, albeit in a slightly different form?
Is this the lesson: given two element declarations inside a choice each with
dfdl:lengthPattern="regex", order the elements so that the element with the
regex that describes the larger set of characters is listed first. Is that the
lesson? If so, we are in deep trouble - how in the world is one to write a
program which determines that one regex describes a larger set of characters
than the other? That is probably possible (in fact, I'm certain that it is
theoretically possible) but practically it is an very hard problem (or at least
an enormous amount of work). Uh oh.
/Roger
-----Original Message-----
From: Steve Lawrence <slawre...@apache.org>
Sent: Wednesday, May 11, 2022 8:10 AM
To: users@daffodil.apache.org
Subject: [EXT] Re: Catalog the causes of the dreaded “left over data” error
message
The regex "[A-Z]{2,20}" says to match between 2 and 20 characters where
only A-Z characters are allowed. Using this regex, Daffodil will scan
the data and stop at the colon character since it does not match A-Z. So
the length of the Identifier element according to the regex is 4 (the
length of "TYPE").
Since the value of the Identifer is "TYPE" is does not fail the nilld or
empty string assertion, and so there is no parse error and the first
choice branch is successful. Because there are no more elements to
parse, the remaining data (i.e. the colon and TEL) are not parsed and
are considered left over data.
When Description is moved to the first branch of the choice, it
successfully parses the "TYPE:" initiator, and then the regex matches
everything after that (i.e. TEL) and it works as expected.
On 5/11/22 7:59 AM, Roger L Costello wrote:
> Another thing that cause the dreaded left over data error message.
>
> I have input containing this field:
>
> TYPE:TEL
>
> That is, the field is initiated by TYPE:
>
> The field has a choice of values: either a string of 2-20 uppercase letters,
> or
> a string 1-56 uppercase letters initiated by TYPE:
>
> Here’s the DFDL schema I used
>
> <xs:choice dfdl:choiceLengthKind="implicit">
> <xs:element name="Identifier" type="non-zero-length-string"
> dfdl:lengthPattern="[A-Z]{2,20}"/>
> <xs:element name="Description" type="non-zero-length-string"
> dfdl:lengthPattern="[A-Z]{1,56}" dfdl:initiator="TYPE:"/>
> </xs:choice>
>
> With that choice and the above input, Daffodil doesn’t process the field and
> reports left over data. As best I can tell, Daffodil uses the first branch of
> the choice, notices that the regex doesn’t contain a colon, and then gives
> up. I
> think.
>
> If I reverse the element declarations, then Daffodil successfully processes
> the
> input.
>
> I guess that I really don’t understand why one works while the other doesn’t.
> Would you explain why Daffodil reports left over data with the first but not
> the
> second, please?
>
> For completeness, here is the simpleType:
>
> <xs:simpleType name="non-zero-length-string" dfdl:lengthKind="pattern">
> <xs:annotation>
> <xs:appinfo source=http://www.ogf.org/dfdl/
> <http://www.ogf.org/dfdl/>>
> <dfdl:assert test="{ fn:nilled(.) or . ne '' }"/>
> </xs:appinfo>
> </xs:annotation>
> <xs:restriction base="xs:string"/>
> </xs:simpleType>
>
> /Roger
>
> *From:* Mike Beckerle <mbecke...@apache.org>
> *Sent:* Tuesday, May 3, 2022 6:32 PM
> *To:* users@daffodil.apache.org
> *Subject:* [EXT] Re: Catalog the causes of the dreaded “left over data” error
> message
>
> Here is a trick used in one schema I've seen:
>
> <*xs**:group *name*="requireNoDataLeft"* >
> <*xs**:sequence* >
> <*xs**:element *name*="data" *type*="tns:tIntField" *dfdl:length*="1"
> *minOccurs*="0"*/>
> <*xs**:sequence* >
> <*xs**:annotation* >
> <*xs**:appinfo *source*="http://www.ogf.org/dfdl/
> <http://www.ogf.org/dfdl/>"* >
> <*dfdl**:assert *test*="{ fn:not(fn:exists(data)) }"
> *message*="Data found where none was expected." */>
> </*xs**:appinfo* >
> </*xs**:annotation* >
> </*xs**:sequence* >
> </*xs**:sequence* >
> </*xs**:group* >
>
> So a group reference to "requireNoDataLeft" states "There cannot be any more
> data available."
>
> This mostly is for the case where there is a surrounding "box" of data such as
> an element with lengthKind 'explicit' and you expect the described contents to
> use up everything in that box.
>
> So if your first choice branch ends with a group ref to "requireNoDataLeft"
> then
> it must consume all available data, and will fail (and backtrack the choice to
> the next one) if there is data available after it.
>
> On Tue, May 3, 2022 at 1:52 PM Roger L Costello <coste...@mitre.org
> <mailto:coste...@mitre.org>> wrote:
>
> The “left over data” error occurs when there is a choice where the first
> branch matches the same data as the second branch and the second branch
> matches a bit more. Input data that matches the second branch fails
> because
> the first branch parses the input and then stops and reports left over
> data.
> See example below.
>
> Is there a workaround? (without manually shuffling the order of the
> branches
> in the choice)
>
> <xs:choice>
> <xs:element name="MilitaryDayTime">
> <xs:complexType>
> <xs:sequence dfdl:separator="">
> <xs:element name="Day" type="non-zero-length-string"
> dfdl:lengthPattern="[0-9]{2}"/>
> <xs:element name="HourTime"
> type="non-zero-length-string"
> dfdl:lengthPattern="[0-9]{2}"/>
> <xs:element name="MinuteTime"
> type="non-zero-length-string"
> dfdl:lengthPattern="[0-9]{2}"/>
> <xs:element name="TimeZone"
> type="non-zero-length-string"
> dfdl:lengthPattern="..."/>
> </xs:sequence>
> </xs:complexType>
> </xs:element>
> <xs:element name="DateTimeGroup">
> <xs:complexType>
> <xs:sequence dfdl:separator="">
> <xs:element name="Day" type="non-zero-length-string"
> dfdl:lengthPattern="[0-9]{2}"/>
> <xs:element name="HourTime"
> type="non-zero-length-string"
> dfdl:lengthPattern="[0-9]{2}"/>
> <xs:element name="MinuteTime"
> type="non-zero-length-string"
> dfdl:lengthPattern="[0-9]{2}"/>
> <xs:element name="TimeZone"
> type="non-zero-length-string"
> dfdl:lengthPattern="..."/>
> <xs:element name="MonthName"
> type="non-zero-length-string"
> dfdl:lengthPattern="…"/>
> <xs:element name="Year" type="non-zero-length-string"
> dfdl:lengthPattern="[0-9]{4}"/>
> </xs:sequence>
> </xs:complexType>
> </xs:element>
> </xs:choice>
>
> *From:* Mike Beckerle <mbecke...@apache.org
> <mailto:mbecke...@apache.org>>
> *Sent:* Monday, May 2, 2022 10:02 AM
> *To:* users@daffodil.apache.org <mailto:users@daffodil.apache.org>
> *Subject:* [EXT] Re: Catalog the causes of the dreaded “left over data”
> error message
>
> I first encountered left-over-data with a dead-simple file format. Just a
> top level element named "records" with a minOccurs="0"
> maxOccurs="unbounded"
> array of elements named "record".
>
> Due to minOccurs="0" such a schema is very happy to "successfully" parse
> zero records, and tell you the entire file contents are "left over data".
>
> I learned one often wants to have minOccurs="1" to force it to at least
> be
> successful on one record.
>
> On Fri, Apr 15, 2022 at 9:48 AM Roger L Costello <coste...@mitre.org
> <mailto:coste...@mitre.org>> wrote:
>
> Hi Folks,
>
> Have you encountered the “left over data” error message? If you’ve
> worked with Daffodil for more than 5 minutes, you undoubtedly have.
>
> The problem with that error message is it gives you absolutely no
> clue
> what’s causing the problem.
>
> Perhaps if we start cataloging the things that triggered the error
> message, then the Daffodil team will be able to provide better
> diagnostics. Here’s my contribution to said catalog.
>
> -----------------------
>
> In recent weeks I have encountered the dreaded “left over data” error
> message twice. After enormous effort I was able to figure out what
> the
> problems were in my DFDL schema. First I need to describe my DFDL
> schema.
>
> My DFDL schema consists of a series of element declarations and
> within
> each element are declarations of subelements:
>
> A
> A.1
> A.2
> …
> B
> B.1
> B.2
> …
> …
>
> Each subelement is of type string and uses a regex to describe the
> subelement’s data (i.e., the subelements use
> dfdl:lengthKind=”pattern”
> and dfdl:lengthPattern=”regex”)
>
> The first time that I got the “left over data” error message I found
> the
> cause was due to this bug in my DFDL schema: a dfdl:lengthPattern
> listed
> the regex alternatives in the wrong order (shortest to longest
> instead
> of longest to shortest). The error message said that Daffodil stopped
> consuming input at element G. The actual element containing the
> regex in
> wrong order was element G.2 (Daffodil stopped consuming input pretty
> near the problem)
>
> After I fixed that bug I immediately got another “left over data”
> error
> at element J. After much more effort I found the bug: a regex
> erroneously had spaces in it. In this case, the error message said
> that
> Daffodil stopped consuming input at element J. The actual element
> containing the regex with spaces was element K.5 (Daffodil stopped
> consuming input pretty far from the problem)
>
> /Roger
>
