🚫 XSD Restrictions – Enforce Data Rules in XML Schema

🧲 Introduction – Why Learn XSD Restrictions?

In XML Schema (XSD), restrictions allow you to control the allowed values of elements and attributes. With restrictions, you can limit lengths, set patterns, define min/max values, and enumerate acceptable options. This ensures your XML documents meet strict business and formatting rules—essential for APIs, forms, and standardized data exchange.

🎯 In this guide, you’ll learn:

• What <xs:restriction> is and how it works
• How to apply restrictions to strings, numbers, and dates
• Examples of enumeration, pattern, minInclusive, length, etc.
• Use cases and best practices for strict XML validation

📘 What Is <xs:restriction>?

<xs:restriction> is used inside <xs:simpleType> to constrain values based on a base data type like xs:string, xs:integer, or xs:date.

🔧 Syntax

<xs:simpleType>
  <xs:restriction base="xs:dataType">
    <!-- constraint facets here -->
  </xs:restriction>
</xs:simpleType>

🔠 String Restrictions

🔹 Example 1 – Limit String Length

<xs:element name="username">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:minLength value="4"/>
      <xs:maxLength value="12"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>

✅ Allows values between 4 and 12 characters long.

🔹 Example 2 – Enforce a Regex Pattern

<xs:element name="email">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:pattern value=".+@.+\..+"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>

✅ Ensures the string looks like an email address.

🔢 Numeric Restrictions

🔹 Example 3 – Range of Integers

<xs:element name="age">
  <xs:simpleType>
    <xs:restriction base="xs:integer">
      <xs:minInclusive value="18"/>
      <xs:maxInclusive value="99"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>

✅ Allows values from 18 to 99 inclusive.

📅 Date Restrictions

🔹 Example 4 – Minimum Date

<xs:element name="eventDate">
  <xs:simpleType>
    <xs:restriction base="xs:date">
      <xs:minInclusive value="2025-01-01"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>

✅ Requires dates on or after January 1, 2025.

🎯 Enumerations

🔹 Example 5 – Restrict to Fixed Values

<xs:element name="status">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="active"/>
      <xs:enumeration value="inactive"/>
      <xs:enumeration value="pending"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>

✅ Only allows "active", "inactive", or "pending".

📚 All String Restriction Facets

📐 All Numeric Restriction Facets

✅ Best Practices for XSD Restrictions

• ✔️ Use enumeration for status flags, categories, or options
• ✔️ Use pattern to validate formats like postal codes, emails, or IDs
• ✔️ Combine minLength and maxLength to control field sizes
• ✔️ For date or age validation, always use minInclusive or maxInclusive
• ❌ Don’t use overly complex regex—keep pattern readable and test it
• ❌ Avoid conflicting restrictions (e.g. minLength > maxLength)

📌 Summary – Recap & Next Steps

XSD restrictions allow you to enforce business rules and data validation at the schema level. With just a few lines, you can catch invalid inputs early and ensure clean, structured data flows.

🔍 Key Takeaways:

• Use <xs:restriction> inside <xs:simpleType> for custom constraints
• Restrict string formats, numeric ranges, and allowable values
• Combine multiple facets for strong validation logic

⚙️ Real-world relevance: Used in XML forms, APIs, e-commerce feeds, digital documents, and any system where data integrity is critical.

❓ FAQs – XSD Restrictions

❓ Can I restrict element and attribute values the same way?
✅ Yes. Use <xs:simpleType> with <xs:restriction> for both.

❓ Can I use multiple restrictions together?
✅ Yes. For example, combine minLength, maxLength, and pattern.

❓ What happens if the value doesn’t match the restriction?
✅ The XML document fails validation.

❓ Are restrictions only for strings?
✅ No. You can restrict numbers, dates, booleans, and even custom types.

❓ Can I use restrictions with global types?
✅ Yes. You can define a restricted type globally and reuse it across elements or attributes.