Miscellaneous

OUTPUT

This command is not implemented in this add-on, since property databases are read-only.

GDL XML EXTENSION

This extension allows reading, writing and editing XML files. It implements a subset of the Document Object Model (DOM) interface. XML is a text file that uses tags to structure data into a hierarchical system, similar to HTML. An XML document can be modeled by a hierarchical tree structure whose nodes contain the data of the document. The following node types are known by the extension:

•Element: what is between a start-tag and an end-tag in the document, or for an empty-element it can be an empty-element tag. Elements have a name, may have attributes, and usually but not necessarily have content. It means that element type nodes can have child nodes. Attributes are held in an attribute list where each attribute has a different name and a text value.

•Text: a character sequence. It cannot have child nodes.

•Comment: text between the comment delimiters: <!-- the comment itself --> . In the text of the comment each ‘-’ character must be followed by a character different from ‘-’. It also means that the following is illegal: <!-- comment ---> . Comment type nodes cannot have child nodes.

•CDATASection: text between the CDATA section delimiters: <![CDATA[ the text itself ]]> . In a CDATA section characters that have special meaning in an XML document need not (and must not) be escaped. The only markup recognized is the closing ‘]]>’. CData section nodes cannot have child nodes.

•Entity-reference: reference to a predefined entity. Such a node can have a read-only subtree and this subtree gives the value of the referenced entity. During the parsing of the document it can be chosen that entity references are translated into text nodes.

On the top level it is obligatory to have exactly one element type node (the root), and there can be several comment type nodes, as well. The document type node of the DOM interface is not available through the extension's interface.

For each node in the tree there is a name and a value string associated whose meanings depend on the type of the node:

Miscellaneous

For each node type the extension defines string keywords that can be passed to the extension in certain instructions:

The success or error code of an OPEN, INPUT or OUTPUT command can be retrieved by the GetLastError instruction of the INPUT command.

Opening XML Document

The OPEN command:

channel = OPEN (filter, filename, parameter_string) filter: file extension. This should be 'XML'.

filename: name and path of the file to open (or create), or an indetifier name if the file is opened through a dialog box and the file's location is given by the user.

parameter_string: a sequence of character flags that determine the open-mode:

•'r': open in read-only mode. In general only the INPUT command can be used.

•'e': entity references are not translated into text nodes in the tree. Without this flag there are no entity-references in the document structure.

•'v': validity check is performed during reading in and writing out. If a DTD exists in the document, the document's structure must agree with it. Without this flag a well-structured but invalid document can be read in and written out without error message.

•'n': create a new file. If the file exists, the open will fail. (After the OPEN the CreateDocument instruction must be the first to execute.)

•'w': overwrite file with empty document if it exists. If it doesn't exist, a new file will be created. (After the OPEN the CreateDocument instruction must be the first to execute.)

•'d': the file is obtained from the user in a dialog box. In later runs it will be associated with the identifier given in the filename parameter of the OPEN command. (If the identifier is already associated to a file, the dialog box will not be opened to the user.)

•'f': the filename parameter contains a full path.

•'l': the file is in the loaded library parts.

channel: used to identify the connection in subsequent I/O commands.

If you want to open an existing XML file for modification, then none of the 'r', 'n' and 'w' flags must be set in the parameter string. Only one of the 'd', 'f' and 'l' flags should be set. If none of these flags is set then filename is considered to be a path relative to the user's documents folder.

Miscellaneous

Reading XML Document

DOM is an object-oriented model that cannot be adapted to a BASIC-like language like GDL directly. To represent the nodes in the hierarchy tree we define position descriptors. When we want to walk through the nodes of the tree, first we have to request a new position descriptor from the extension. Originally a new descriptor points to the root element. The descriptor is in fact a 32 bit identification number whose value has no interest for the GDL script. The position it refers to can be changed as we move from one node in the tree to another.

The INPUT command:

INPUT (ch, recordID, fieldID, var1, var2...) ch: channel returned by the OPEN command

recordID: instruction name plus parameters

fieldID: usually a position descriptor var1, var2,...: optional list of variables receiving returned data. INPUT instructions:

1GetLastError: retrieve the result of the last operation recordID: "GetLastError"

fieldID: ignored

return values:

var1: error code / ok

var2: the explanation text of error / ok

2NewPositionDesc: request for a new position descriptor recordID: "NewPositionDesc"

fieldID: ignored

return value: var1: the new position descriptor (initially refers to the root)

3CopyPositionDesc: request for a new position descriptor whose starting node is taken from another descriptor. recordID: "CopyPositionDesc"

fieldID: an existing position descriptor

return value: var1: the new position descriptor (initially refers to where the descriptor given in fieldID refers to)

4ReturnPositionDesc: when a position descriptor is no longer needed. recordID: "ReturnPositionDesc"

fieldID: the position descriptor.

Call this instruction when a position descriptor received from the NewPositionDesc or CopyPositionDesc instructions is no longer used.

Miscellaneous

5MoveToNode: change the position of a descriptor. (and retrieve the data of the new node) This instruction can be used for navigating in the tree hierarchy.

recordID: "MoveToNode searchmode nodename nodetype nodenumber" fieldID: position descriptor

searchmode (or movemode): the nodename parameter must contain a path that determines an element or entity reference node in the xml document.

The path is relative to the node given in fieldID. The delimiter is the ':' character (which is otherwise an accepted character in an element's name so this doesn't work for all cases). The '..' string in the path means a step to the parent node. The starting node can be different from an element or entity reference node, in which case the path must begin with '..' to step back. If there are several element nodes on the same level with the same name then the first one is chosen.

For the following move-modes the rest of the parameters must not be present: ToParent: moves to the parent of the node given in fieldID. ToNextSibling: moves to the next node on the same level.

ToPrevSibling: moves to the previous node on the same level. ToFirstChild: moves to the first descendant of the fieldID node. ToLastChild: moves to the last descendant of the fieldID node.

The following are the search-modes for which the rest of the parameters may occur, but they have default values if not present: FromNextSibling: searching starts from the next node on the same level and it moves forward.

FromPrevSibling: searching starts from the node before fieldID and it moves backward on the same level. FromFirstChild: searching starts from the first descendant of the fieldID node and moves forward. FromLastChild: searching starts from the last descendant of the fieldID node and moves backward.

nodename: the searching considers those nodes only whose name or value matches nodename. The * and ? characters in nodename are considered as wildcard characters. For element and entity reference type nodes the name is compared, while for text, comment and CDATA section nodes the value is compared. Default value: *

nodetype: the searching considers those nodes only whose type is allowed by nodetype. The * means all types are allowed. Otherwise the type keywords can be combined with the + character to form the nodetype (it must be one word without spaces, like TXT+CDATA.) The default value is *

nodenumber: if there are several matching nodes, this gives the number of the searched node in the sequence of matching nodes. (Starts from 1) Default value: 1

return values:

var1: name of the node var2: value of the node

var3: type keyword of the node

Miscellaneous

Example:

We want to move backwards on the same level to the 2nd node that is an element or an entity reference and whose name starts with K:

INPUT (ch, "MoveToNode FromPrevSibling K* ELEM+EREF 2", posDesc, name, val, type)

6GetNodeData: retrieve the data of a given node. recordID: "GetNodeData"

fieldID: the position descriptor return values:

var1: name of the node var2: value of the node

var3: type keyword of the node

7NumberofChildNodes: gives the number of child nodes of a given node recordID: "NumberofChildNodes nodetype nodename" fieldID: position descriptor

The following optional parameters can narrow the set of child nodes considered: nodetype: allowed node types as defined in the MoveToNode instruction nodename: allowed node names or values as defined in the MoveToNode instruction

return values:

var1: number of child nodes

8NumberofAttributes: returns the number of attributes of an element node. recordID: "NumberofAttributes attrname"

fieldID: position descriptor (must refer to an element node)

attrname: if present, it can narrow the set of attributes considered as only those attributes will be counted whose names (and not the values) match attrname. In attrname the * and ? characters are considered wildcard characters.

return values:

var1: number of attributes