Why do we need namespaces in xml

Any arbitrary text string can be used as a namespace prefix; since there is no special meaning, any text string will do. However, the URI must be universally unique.

Since the URL is not actually accessed, it is not a problem if the file, etc. Understand that a URI represents nothing more than a logical namespace name. The namespace declaration scope is the scope for which the namespace prefix declared in a namespace declaration can be described. This scope covers the element and element content from the element start tag to the end tag for which the namespace declaration has been written. A namespace prefix can be written for an element or descendant element for which a namespace has been declared, or for an attribute defined therein.

A separate namespace declaration can be made for the descendant element of an element for which a namespace declaration has already been made, and a different namespace prefix within that scope can be used as well. In addition to highest-order elements, namespace declarations can also be made in discrete sections. However, the same namespace declaration would have to be repeated many times, making the XML document difficult to follow.

In this type of situation, it is best to make a collective set of namespace declarations in the highest-order element, as shown in the LIST1 example. Attributes can either belong to the same namespace of the element for which the attribute is defined, or belong to a completely different namespace than that to which the element belongs. The definition for an attribute that belongs to a namespace is the same as that for elements, with the "namespacePrefix:" notation coming before the attribute name.

If no namespace prefix is provided for the attribute name, the attribute will not belong to any namespace. What must be noted here is that under the XML 1. However, for XML documents conforming to the Namespaces in XML specification, the combination of namespace identifier and attribute name is what determines whether an attribute is duplicated. Accordingly, if the namespace identifier is different, attributes having the same attribute name are considered to be different.

A "default namespace" is a namespace declaration that does not use a namespace prefix See Figure 11 for notation method. The scope of the default namespace is the element for which the namespace was declared and the related content, just as with the namespace scope discussed earlier. The benefit of using a default namespace is that the namespace prefix can be omitted. For example, when adding a new namespace to an existing XML document, writing a namespace prefix for each element to which the new namespace will be applied involves a tremendous amount of tedious work.

The larger the XML document, the greater the labor involved, and the greater the likelihood of notation errors. In this type of situation, adding only a default namespace declaration to the XML document in question eliminates the need to write a namespace prefix for each and every element, saving a lot of time. On the other hand, there are drawbacks. One drawback is that omitting the namespace prefix makes it more difficult to understand which element belongs to which namespace, and which namespace is applicable.

In addition, programmers should remember that when a default namespace is declared, the namespace is applied only to the element, and not to any attributes. A default namespace can be overwritten partially by declaring a completely different default namespace within the scope of the original default namespace.

Namespaces can be declared either explicitly or by default. With an explicit declaration, you define a shorthand, or prefix, to substitute for the full name of the namespace. You use this prefix to qualify elements belonging to that namespace. Explicit declarations are useful when a node contains elements from different namespaces. A default declaration declares a namespace to be used for all elements within its scope, and a prefix is not used.

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