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XSD Indicators

Through indicators, we can control how elements are used in the document.

Indicators

There are seven indicators:

Order Indicators:

Occurrence Indicators:

Group Indicators:

Order Indicators

Order indicators are used to define the sequence of elements.

All Indicator

The <all> indicator specifies that child elements can appear in any order, and each child element must appear only once:

Note: When using the <all> indicator, you can set <minOccurs> to 0 or 1, and <maxOccurs> can only be set to 1 (later explained are <minOccurs> and <maxOccurs>).

Choice Indicator

The <choice> indicator specifies that either one child element or another can appear (but not both):

Sequence Indicator

The <sequence> indicator specifies that child elements must appear in a specific order:

Occurrence Indicators

Occurrence indicators are used to define the frequency of an element's appearance.

Note: For all "Order" and "Group" indicators (any, all, choice, sequence, group name, and group reference), the default values for maxOccurs and minOccurs are both 1.

maxOccurs Indicator

The <maxOccurs> indicator can specify the maximum number of times an element can appear:

The example above indicates that the child element "child_name" can appear at least once (the default value for minOccurs is 1) and up to 10 times within the "person" element.

minOccurs Indicator

The <minOccurs> indicator can specify the minimum number of times an element can appear:

The example above indicates that the child element "child_name" can appear at least 0 times and up to 10 times within the "person" element.

Tip: To make an element's occurrence unlimited, use the declaration maxOccurs="unbounded":

A Practical Example:

An XML file named "Myfamily.xml":

This XML file contains a root element named "persons". Inside this root element, we define three "person" elements. Each "person" element must contain one "full_name" element and can contain up to five "child_name" elements.

Here is the schema file "family.xsd":

Group Indicators

Group indicators are used to define related batches of elements.

Element Group

Element groups are defined through the group declaration:

You must define an all, choice, or sequence element inside the group declaration. The following example defines a group named "persongroup", which specifies a set of elements that must appear in an exact order:

After defining the group, you can reference it in another definition:

Attribute Group

Attribute groups are defined through the attributeGroup declaration:

The following example defines an attribute group named "personattrgroup":

After defining the attribute group, you can reference it in another definition, like this:

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