XML XSD Data Types

How it works

Use decimal for an exact base-ten measurement, an integer subtype for a count and date for a calendar date. Some date forms allow a timezone and others do not require one; a business contract may need a stricter policy. Boolean accepts true, false, 1 and 0 in XSD, which is broader than this exchange’s earlier true/false application flag. list creates whitespace-separated sequences, and anyURI validates a lexical form without fetching a resource.

Run the code

Use Python 3 with lxml 6.1.1 in a separate virtual environment. The complete listing embeds its own XML and any schema or stylesheet; run python datatype-values.py. It does not need Apache or MySQL. The shared restrictive parse function rejects declarations for untrusted input. The trusted DTD/entity and streaming lessons explicitly explain their separate fixed-input boundaries.

Download the complete datatype-values.py source. Keep each lab in its own folder. Sources are served as text, not as public executable server scripts. Review the starting setup.

Example

from lxml import etree as E

class DenyExternal(E.Resolver):
    def resolve(self, url, public_id, context):
        raise ValueError("External resources are disabled")

def parse(text):
    if "<!DOCTYPE" in text.upper() or "<!ENTITY" in text.upper():
        raise ValueError("Declarations are disabled for untrusted XML")
    parser = E.XMLParser(resolve_entities=False, load_dtd=False,
                         no_network=True, huge_tree=False)
    parser.resolvers.add(DenyExternal())
    return E.fromstring(text.encode("utf-8"), parser)

source = "<sample count=\"12\" collected=\"2026-10-31\" tags=\"dry local\"/>"
root = parse(source)
schema_source = "<xs:schema xmlns:xs=\"http://www.w3.org/2001/XMLSchema\" ><xs:simpleType name=\"Tags\"><xs:list itemType=\"xs:token\"/></xs:simpleType><xs:element name=\"sample\"><xs:complexType><xs:attribute name=\"count\" type=\"xs:nonNegativeInteger\" use=\"required\"/><xs:attribute name=\"collected\" type=\"xs:date\" use=\"required\"/><xs:attribute name=\"tags\" type=\"Tags\"/></xs:complexType></xs:element></xs:schema>"
contract = E.XMLSchema(parse(schema_source))
print(contract.validate(root))

Expected result

True

The record combines a non-negative count, a real calendar date and a token list. Change the count to -1 or the month to 19 and validation fails. These checks are about the value contract, not whether the collection happened in real life.