How to dynamically specify the length and datatype of an element?

[Costello, Roger L.]

Hello DFDL community!

I am creating a DFDL schema to parse dBase files.

A dBase file consists of a list of records. Each record consists of a list of 
fields. Prior to the list of records is a header which describes each record 
field: the field's name, the length of the field's value, and its datatype 
(string, date, numeric, boolean, etc.). For example, I have a dBase file 
containing railway data and the file looks like this (albeit in binary):

Field-descriptor-array
    Field
        name: station-name
        length: 254
        datatype: string
    Field
        name: line
        length: 100
        datatype: string
    Field
        name: isActive
        length: 1
        datatype: boolean

Here is a record:

    Van Dorn Street
    blue
    T

Ideally, parsing the dBase file would yield this XML:

    <record>
        <station-name>Van Dorn Street</station-name>
        <line>blue</line>
        <isActive>true</isActive>
    </record>
    
However, that requires element names be dynamically generated, which is not 
currently supported. So, instead I can design the DFDL schema to generate this 
XML:

    <record>
        <field>Van Dorn Street</field>
        <field>blue</field>
        <field>true</field>
    </record>

That will require the DFDL schema to calculate the number of <field> elements:

    <xs:element         name="field" 
                minOccurs="0" 
                maxOccurs="unbounded" 
                dfdl:occursCountKind="expression" 
                dfdl:occursCount="count{../../Field-descriptor-array/Field}" 
                ...

Does this seem reasonable thus far?

Now I am stuck: how to specify the length and the datatype of each field 
element? The i'th <field> element must have a length and datatype as specified 
in the i'th Field (which are in the header section). For the example above, the 
first <field> element must be a string with length 254 characters, the second 
<field> element must be a string with length 100 characters, and the third 
<field> element must be a boolean with length 1 byte. How do I dynamically 
specify length and datatype?

/Roger