Introduction
The simplest way of thinking of ASN.1 Information Object Classes is to regard them as a way to represent IDL specification in ASN.1 using concepts derived from the relational databases theory and SQL syntax in particular.
The concepts used in ASN.1 are more flexible than the ones used in IDL, because, continuing the analogy, they allow to "customize grammar" of the "IDL specification". ASN.1 encoding rules are used as a transfer syntax for remote invocations that resemble CORBA/IIOP.
In the light of this comparison, we can draw an approximate analogy between concepts used in Information Object Classes and SQL and IDL concepts as shown in Table 1.
| ASN.1 term | Analogy in SQL | Analogy in IDL | |
|---|---|---|---|
|
Information Object Class (IOC) |
SQL table structure descriptor (CREATE TABLE statement) |
IDL grammar specification (BNF rules) |
|
|
IOC field declaration |
SQL table column descriptor in CREATE TABLE statement (type of a column) |
IDL grammar production |
|
|
Information Object (IO) |
SQL table row (INSERT INTO statement) |
IDL operation declaration |
|
|
IO field definition |
Cell of SQL table row in INSERT INTO statement (cell value) |
Portion of IDL operation declaration, typically related to declaration of an operation type code, parameter list, operation return value, or list of exceptions |
|
|
Information Object Set (IOS) (collection of Information Objects) |
Completely defined SQL table (collection of rows) (see Note 1) |
IDL interface definition (collection of operations) |
|
|
ASN.1 data type using references to IOC fields parameterized with IOS (typically a collection of semantically related types designating request, response, and exception, all parameterized with the same IOS) |
- |
High-level format (grammar specification) of a frame (marshalling buffer) carrying CORBA request, response, or exception |
|
|
ASN.1 encoding rules and transfer syntaxes (BER, PER) |
- |
Low-level encoding of requests, responses and exception indicators suitable for physical transfer over the medium |
|
|
Note 1. The analogy between IOS and an SQL table is not quite correct. SQL permits only one instance of a table of given type (OPERATION in the example below), while ASN.1 permits multiple Information Object Sets derived from the same Information Object Class, what should be most correctly related to multiple instances of the same table in terms of SQL (OPERATION in the example below). |
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Read more about this topic: Information Object Class (ASN.1)
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