explain the difference betn comma and pipe symbols in deciding how child elements are used within an XML document
Answers
Structure of a Document Type Definition
Explanation:
The structure of a DTD consists of a Document Type Declaration, elements, attributes, entities, and several other minor keywords. We will take a look at each of these topics, in that order. As we progress from topic to topic, we will follow a mini case study about the use of XML to store employee records by the Human Resources department of a fictitious company.
Our coverage of the DTD structure shall begin with the Document Type Declaration.
The Document Type Declaration
In order to reference a DTD from an XML document, a Document Type Declaration must be included in the XML document. Listings 3.1, 3.2, and 3.3 gave some examples and brief explanations of using a Document Type Declaration to reference a DTD. There may be one Document Type Declaration per XML document. The syntax is as follows:
<!DOCTYPE rootelement SYSTEM | PUBLIC DTDlocation [ internalDTDelements ] >
The exclamation mark (!) is used to signify the beginning of the declaration.
DOCTYPE is the keyword used to denote this as a Document Type Definition.
rootelement is the name of the root element or document element of the XML document.
SYSTEM and PUBLIC are keywords used to designate that the DTD is contained in an external document. Although the use of these keywords is optional, to reference an external DTD you would have to use one or the other. The SYSTEM keyword is used in tandem with a URL to locate the DTD. The PUBLIC keyword specifies some public location that will usually be some application-specific resource reference.
internalDTDelements are internal DTD declarations. These declarations will always be placed within opening ([) and closing (]) brackets.
Answer:
These are two symbols used to separate child elements are
Explanation:
1 ( ,) comma the elements must appear strictly in the order in which they are defined in the elements declaration.
2 ( |) the elements may appear one or more time in any order