I am a little confused about what these tagas are to represent.
Could I get a little help on where to read up and get clarification?
They don't represent anything, certainly not any more than the address on
your house represents you. Instead they identify fields by being unique
enough that one can figure out which field is which. Knowing what's unique
enough is a more complicated matter since it depends upon things you
probably aren't yet familiar with. Let's instead take a simple and not too
atypical an example:
Z ::= SEQUENCE {
msg1 [0] SEQUENCE {
aa [0] INTEGER,
bb [1] BOOLEAN,
cc [2] PrintableString
},
msg2 [1] SEQUENCE {
dd [0] INTEGER,
ee [1] BOOLEAN,
ff [2] OCTET STRING
}
}
Note that there are two [0] tags for INTEGERs and one [0] tag for
SEQUENCE. You might question how one tells them apart since they are all
[0]s. The answer is that you discern them from the context. Thus if I see
a [0] within a [0], it's aa, while if I see a [0] within a [1], it's dd.
Actually, in the example above, even Z has a tag although you can't see
it. It's the default tag [UNIVERSAL 16]. So, to be more precise,
- if you see a [0] within a [0] within a [UNIVERSAL 16], it's aa;
- if you see a [0] within a [1] within a [UNIVERSAL 16], it's dd; and
- if you see a [0] within a [UNIVERSAL 16], it msg1.
It looks like you could use some basics. Permit me to suggest
http://www.oss.com/asn1/booksintro.html
where you can download two ASN.1 reference manuals. They are both
comprehensive, although with different emphasis. Each has its own fans,
but both are very good.
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OSS Nokalva Fax : 1-614-388-4156
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