64 lines
2.3 KiB
Markdown
64 lines
2.3 KiB
Markdown
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# Object-oriented representation of the DDL (OO-DDL) {#page_oo_ddl}
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# Introduction
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To facilitate the handling of DDL hierarchies there is an object-oriented
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approach of representation, called OO-DDL.
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Within the class structure of OO-DDL every node type inside the DDL definition
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is representated by an own class.
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**Note:**
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These classes are associated by using the GoF design patterns "Visitor",
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"Decorator", and "Factory Method".
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The main classes are described in the following section.
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# Structure of classes
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The basic interface of nearly all classes of the OO-DDL is `ddl::IDDL`.
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The root element of every DDL structure is an instance of
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`ddl::cDDLDescription`. For example a DDL Definition File may be
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represented by `cDDLDescription`. This object holds references to the main
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parts like the header (`ddl::cDDLHeader`) or the datatypes
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(`ddl::IDDLDataType`). For further information on all available OO-DDL
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classes see the SDK documentation of `ddl::IDDL`.
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Every link between DDL-representing objects is realized as pointer to the
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according object. So lots of string comparisons for matching e.g. child
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elements could be removed.
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# Building up - using ddl::IDDLFactoryMethod
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For all creation tasks concerning OO-DDL implementations of the interface
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`IDDLFactoryMethod` are used. A basic implementation of `IDDLFactoryMethod`
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is `ddl::cDDLImporter`.
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# Processing DDL - using ddl::IDDLVisitor
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For every task of processing DDL implementations of `ddl::IDDLVisitor` are
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used. Utilizing this interface the DDL-representing hierarchy can be walked
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through and appropriate actions may be taken. The basic implementation of
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`IDDLVisitor` is `ddl::cDDLPrinter`.
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# The Correlation Between OO-DDL and DDL.
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Every tag and some attributes in the DDL have a correspondent in the OO-DDL.
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The following table shows the OO-DDL classes with their matching DDL tag or attribute:
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|DDL Tag/Attribute|OO-DDL Class|
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|--- |--- |
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|`<adtf:ddl>`|cDDLDescription|
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|`<header>`|cDDLHeader|
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|`<ext_declaration>`|cDDLExtDeclaration|
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|`<baseunit>`|cDDLBaseunit|
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|`<prefix>`|cDDLPrefix|
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|`<unit>`|cDDLUnit|
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|`<refUnit>`|cDDLRefUnit|
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|`<datatype>`|cDDLDataType|
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|`<enum>`|cDDLEnum|
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|`<struct>`|cDDLComplex|
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|`<element>`|cDDLElement|
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|alignment=xxx|cDDLAlignment|
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|byteorder=xxx|cDDLByteorder|
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|`<stream>`|cDDLStream|
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|`<struct>` (within a `<stream>` tag)|cDDLStreamStruct|
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