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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Chapter 2 — XML and XSD — The Technological Basis</title>
<link rel="icon" type="image/png" href="FundsXML-Logo.png">
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<nav class="chapter-nav" aria-label="Chapter navigation"><a class="cn-prev" href="Chapter01.html">‹ Chapter 1</a><a class="cn-toc" href="index.html">Contents</a><a class="cn-next" href="Chapter03.html">Chapter 3 ›</a></nav>
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<div class="chapter-meta">Part I — Foundations · Chapter 2</div>
<h1>XML and XSD — The Technological Basis<span class="subtitle">Foundational knowledge for working with FundsXML</span></h1>
<hr>
<h2>2.1 From "Why" to "How": A Short Hop</h2>
<p>Chapter 1 built the case for a single, shared standard for fund data. It did so deliberately without a single line of XML: the argument there was economic and operational, not technical. This chapter begins the technical half of the journey. It introduces XML and XSD — the two technologies on which FundsXML rests — and it does so from the perspective of a fund professional who needs to <em>read</em>, <em>validate</em>, <em>query</em>, and <em>transform</em> fund-data documents, not from the perspective of a software engineer building an XML parser from scratch.</p>
<p>Return, for a moment, to the Europa Growth Fund. At the end of Chapter 1, the operations team had decided — at least in principle — to adopt FundsXML as the canonical representation of its fund-product data. The next question on the team's mind is very practical: <em>what does such a FundsXML file actually look like?</em> When a colleague drops a 2-megabyte document on the desk and says "this is the monthly delivery", what should we expect to see? How do we confirm that the file is correct before we send it out? How do we extract the twenty fields that the fact-sheet engine needs? How do we turn the same file into the CSV that a Swiss distributor still insists on?</p>
<p>Those are the questions this chapter answers in general terms. Chapter 3 will then apply the answers to the specific shape of the FundsXML schema; Chapters 4 to 9 will walk through the schema module by module; Chapter 10 will explain the two-stage validation discipline that keeps production deliveries healthy. Everything from here on depends on the vocabulary of XML and XSD being second nature, and so the investment of thirty pages at this point is repaid many times over in the chapters that follow.</p>
<p>The chapter is deliberately practical. XML is a large specification with many corners that FundsXML does not use, and this book does not visit them. Where a topic is genuinely optional for a fund practitioner, we say so and move on. Where a topic matters every day — element-versus-attribute design, schema validation, namespaces, the basic XPath idiom — we spend the time.</p>
<p>By the end of this chapter, you should be able to:</p>
<ul>
<li>read and write well-formed XML documents and recognise the most common syntactic mistakes;</li>
<li>explain the purpose of XML namespaces and interpret a namespaced document;</li>
<li>read an XSD schema and map its declarations to the instance documents they constrain;</li>
<li>describe the difference between well-formedness and schema validity, and between schema validation and business-rule validation;</li>
<li>navigate an XML document with elementary XPath expressions;</li>
<li>understand what an XSLT transformation does and follow a simple stylesheet end to end;</li>
<li>name the tools a fund-industry practitioner typically uses for day-to-day XML work and know which later chapter treats each of them in depth.</li>
</ul>
<p>No prior XML experience is assumed. Readers who already write XSLT 3.0 in their sleep may skim the first half of the chapter and rejoin us at §2.10.</p>
<hr>
<h2>2.2 XML in One Page</h2>
<p>At its heart, XML is a notation for writing down trees of data as plain text. A document is a single tree with a single root. Every branch of the tree is an <em>element</em>. Each element has a name, may carry <em>attributes</em>, may contain other elements, and may contain text. That is essentially the whole data model; everything else in this chapter is either syntax that expresses this model or a schema language that constrains it.</p>
<p>The Europa Growth Fund, stripped to its bare essentials, looks like this in real FundsXML:</p>
<pre><code><span class="tok-decl"><?xml version="1.0" encoding="UTF-8"?></span>
<span class="tok-punct"><</span><span class="tok-tag">FundsXML4</span> <span class="tok-attr">xmlns:xsi</span><span class="tok-punct">=</span><span class="tok-string">"http://www.w3.org/2001/XMLSchema-instance"</span>
<span class="tok-attr">xsi:noNamespaceSchemaLocation</span><span class="tok-punct">=</span><span class="tok-string">"FundsXML4.xsd"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ControlData</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">UniqueDocumentID</span><span class="tok-punct">></span>EGF-20260331-001<span class="tok-punct"></</span><span class="tok-tag">UniqueDocumentID</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">DocumentGenerated</span><span class="tok-punct">></span>2026-04-01T06:47:13Z<span class="tok-punct"></</span><span class="tok-tag">DocumentGenerated</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Version</span><span class="tok-punct">></span>4.2.8<span class="tok-punct"></</span><span class="tok-tag">Version</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ContentDate</span><span class="tok-punct">></span>2026-03-31<span class="tok-punct"></</span><span class="tok-tag">ContentDate</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">DataSupplier</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">SystemCountry</span><span class="tok-punct">></span>LU<span class="tok-punct"></</span><span class="tok-tag">SystemCountry</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Short</span><span class="tok-punct">></span>EAM<span class="tok-punct"></</span><span class="tok-tag">Short</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Name</span><span class="tok-punct">></span>Europa Asset Management S.A.<span class="tok-punct"></</span><span class="tok-tag">Name</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Type</span><span class="tok-punct">></span>IC<span class="tok-punct"></</span><span class="tok-tag">Type</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">DataSupplier</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">DataOperation</span><span class="tok-punct">></span>INITIAL<span class="tok-punct"></</span><span class="tok-tag">DataOperation</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Language</span><span class="tok-punct">></span>en<span class="tok-punct"></</span><span class="tok-tag">Language</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">ControlData</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Funds</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Fund</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Identifiers</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">LEI</span><span class="tok-punct">></span>549300ABCDEFGHIJ1234<span class="tok-punct"></</span><span class="tok-tag">LEI</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Identifiers</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Names</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">OfficialName</span><span class="tok-punct">></span>Europa Growth Fund<span class="tok-punct"></</span><span class="tok-tag">OfficialName</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Names</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Currency</span><span class="tok-punct">></span>EUR<span class="tok-punct"></</span><span class="tok-tag">Currency</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">SingleFundFlag</span><span class="tok-punct">></span>true<span class="tok-punct"></</span><span class="tok-tag">SingleFundFlag</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">FundDynamicData</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">TotalAssetValues</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">TotalAssetValue</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">NavDate</span><span class="tok-punct">></span>2026-03-31<span class="tok-punct"></</span><span class="tok-tag">NavDate</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">TotalAssetNature</span><span class="tok-punct">></span>OFFICIAL<span class="tok-punct"></</span><span class="tok-tag">TotalAssetNature</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">TotalNetAssetValue</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Amount</span> <span class="tok-attr">ccy</span><span class="tok-punct">=</span><span class="tok-string">"EUR"</span><span class="tok-punct">></span>464552848.78<span class="tok-punct"></</span><span class="tok-tag">Amount</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">TotalNetAssetValue</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">TotalAssetValue</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">TotalAssetValues</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">FundDynamicData</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">SingleFund</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ShareClasses</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ShareClass</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Identifiers</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ISIN</span><span class="tok-punct">></span>LU1234567890<span class="tok-punct"></</span><span class="tok-tag">ISIN</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Identifiers</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Names</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">OfficialName</span><span class="tok-punct">></span>Europa Growth Fund I EUR Acc<span class="tok-punct"></</span><span class="tok-tag">OfficialName</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Names</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Currency</span><span class="tok-punct">></span>EUR<span class="tok-punct"></</span><span class="tok-tag">Currency</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">ShareClass</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ShareClass</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Identifiers</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ISIN</span><span class="tok-punct">></span>LU1234567892<span class="tok-punct"></</span><span class="tok-tag">ISIN</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Identifiers</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Names</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">OfficialName</span><span class="tok-punct">></span>Europa Growth Fund R CHF Acc Hedged<span class="tok-punct"></</span><span class="tok-tag">OfficialName</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Names</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Currency</span><span class="tok-punct">></span>CHF<span class="tok-punct"></</span><span class="tok-tag">Currency</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">ShareClass</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">ShareClasses</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">SingleFund</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Fund</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Funds</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">FundsXML4</span><span class="tok-punct">></span>
</code></pre>
<p>Three observations are worth making before going further. First, this is a minimal but <strong>schema-valid</strong> FundsXML document — it validates against the real <code>FundsXML4.xsd</code> without errors (Appendix D contains the full set of progressively richer examples). The document carries a <a href="https://fundsxml.github.io/index.html?xpath=/FundsXML4/ControlData" target="_blank"><code>ControlData</code></a> envelope that identifies the delivery, followed by a <a href="https://fundsxml.github.io/index.html?xpath=/FundsXML4/Funds" target="_blank"><code>Funds</code></a> block with a single fund and its two share classes. Chapters 4 and 5 explain every element in this document in depth; for now, read it as a map of the territory ahead.</p>
<p>Second, the document is entirely human-readable. A fund operations analyst can inspect it with any text editor and, after a minute of orientation, understand it without tooling. The element names — <code>ControlData</code>, <code>Fund</code>, <code>Names</code>, <code>OfficialName</code>, <code>Currency</code>, <code>ShareClass</code>, <code>ISIN</code> — read almost like a structured form. This readability is one of XML's enduring strengths and is a large part of why regulators and industry bodies have chosen XML-based formats for durable disclosures.</p>
<p>Third, the tree structure is visible in the indentation but does not depend on it. XML ignores most whitespace between elements; the indentation is a convenience for humans. Parsers see the same tree regardless of how the file is formatted.</p>
<p>A note on the examples in this chapter. The document above and the share-class examples later in this chapter are real FundsXML validated against the 4.2.8 schema. A small number of examples in the XML-syntax and namespace sections (§2.3–§2.5) use simplified, hand-rolled elements to illustrate general XML concepts in isolation; where this is the case, the text says so. Every example that claims to be FundsXML is schema-valid.</p>
<p>With this much in hand, we can now be precise about the syntactic rules that make a document well-formed.</p>
<hr>
<h2>2.3 XML Syntax — Elements, Attributes, Text</h2>
<h3>2.3.1 Well-formedness</h3>
<p>An XML document is <em>well-formed</em> if it obeys a small number of strict rules. A well-formed document can be parsed by any conforming XML processor, regardless of whether it matches any schema. The rules are:</p>
<ul>
<li><strong>Exactly one root element.</strong> The outermost pair of tags encloses everything. In the Europa Growth Fund example above, <a href="https://fundsxml.github.io/index.html?xpath=/FundsXML4" target="_blank"><code><FundsXML4></code></a> is the root.</li>
<li><strong>Every start tag has a matching end tag.</strong> <code><Name>Europa Growth Fund</Name></code> is well-formed; <code><Name>Europa Growth Fund</code> is not.</li>
<li><strong>Elements nest properly.</strong> <code><a><b></b></a></code> is well-formed; <code><a><b></a></b></code> is not.</li>
<li><strong>Element and attribute names are case-sensitive.</strong> <code><Fund></code> and <code><fund></code> are different elements.</li>
<li><strong>Attribute values are always quoted.</strong> Single or double quotes are both allowed: <code>id="EGF-001"</code> and <code>id='EGF-001'</code> are equivalent.</li>
<li><strong>Five characters are reserved and must be escaped</strong> when they appear as text: <code><</code> becomes <code>&lt;</code>, <code>></code> becomes <code>&gt;</code>, <code>&</code> becomes <code>&amp;</code>, <code>"</code> becomes <code>&quot;</code>, and <code>'</code> becomes <code>&apos;</code>.</li>
</ul>
<p>An element with no content can be written as <code><ShareClass></ShareClass></code> or, equivalently, as the empty-element form <code><ShareClass/></code>. Parsers treat the two forms as identical.</p>
<p>A well-formed document is not necessarily a <em>useful</em> document: it may still violate a schema, contain the wrong fields, or carry impossible values. Well-formedness is the bottom rung of the validation ladder, not the top.</p>
<h3>2.3.2 Elements versus attributes</h3>
<p>One of the oldest debates in XML design is the choice between expressing a piece of information as a child element or as an attribute. Consider two hypothetical ways of writing a fund's base currency (these are general XML illustrations, not FundsXML elements):</p>
<pre><code><span class="tok-comment"><!-- As a child element --></span>
<span class="tok-punct"><</span><span class="tok-tag">Fund</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">BaseCurrency</span><span class="tok-punct">></span>EUR<span class="tok-punct"></</span><span class="tok-tag">BaseCurrency</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Fund</span><span class="tok-punct">></span>
<span class="tok-comment"><!-- As an attribute --></span>
<span class="tok-punct"><</span><span class="tok-tag">Fund</span> <span class="tok-attr">baseCurrency</span><span class="tok-punct">=</span><span class="tok-string">"EUR"</span><span class="tok-punct">/></span>
</code></pre>
<p>Both carry the same information. The working rules of thumb, applied consistently throughout FundsXML and throughout the examples in this book, are:</p>
<ul>
<li><strong>Use elements for data, attributes for metadata.</strong> The currency of a fund is data; the version of a schema or the identifier of a document is metadata about the document itself.</li>
<li><strong>Use elements when the value may later need sub-structure.</strong> A fund name today is a string; tomorrow it might need a language tag or a sort form. Elements can grow children; attributes cannot.</li>
<li><strong>Use attributes for values that qualify the enclosing element without being part of its content.</strong> The <code>id</code> on a record, the unit of a measurement, the version of a format.</li>
<li><strong>Prefer elements when in doubt.</strong> FundsXML leans heavily towards elements, and the habit of reaching for an element first is the safer default for a practitioner.</li>
</ul>
<p>Illustrated on a hypothetical share-class element (not the actual FundsXML element, which uses <code>Identifiers/ISIN</code> and <code>Names/OfficialName</code> instead):</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">ShareClass</span> <span class="tok-attr">id</span><span class="tok-punct">=</span><span class="tok-string">"EGF-001-ACC-EUR"</span> <span class="tok-attr">currency</span><span class="tok-punct">=</span><span class="tok-string">"EUR"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">ISIN</span><span class="tok-punct">></span>LU0000000001<span class="tok-punct"></</span><span class="tok-tag">ISIN</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Name</span> <span class="tok-attr">xml:lang</span><span class="tok-punct">=</span><span class="tok-string">"en"</span><span class="tok-punct">></span>Europa Growth Fund, Accumulating, EUR<span class="tok-punct"></</span><span class="tok-tag">Name</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Name</span> <span class="tok-attr">xml:lang</span><span class="tok-punct">=</span><span class="tok-string">"de"</span><span class="tok-punct">></span>Europa Growth Fund, Thesaurierend, EUR<span class="tok-punct"></</span><span class="tok-tag">Name</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">ShareClass</span><span class="tok-punct">></span>
</code></pre>
<p>Here <code>id</code> and <code>currency</code> are qualifiers — they tell us <em>which</em> share class and in <em>what unit</em> — while the <code>ISIN</code> and the two <code>Name</code> elements carry the share class's own data. Note how the element form of <code>Name</code> naturally accommodates two languages; an attribute form could not. The real FundsXML schema resolves this design question consistently in favour of elements: the currency is always a child element <code><Currency>EUR</Currency></code>, not an attribute.</p>
<h3>2.3.3 Text, mixed content, CDATA, and comments</h3>
<p>Element content falls into three categories. An element may contain only other elements (<em>element-only content</em>, the usual case for structured data such as a portfolio), only text (<em>text-only content</em>, typical for leaf fields such as <code><ISIN></code>), or a mixture (<em>mixed content</em>, in which text and child elements are interleaved). Mixed content is common in fact-sheet prose and regulatory narrative text, but rare in portfolio and transaction structures.</p>
<p>A short fact-sheet paragraph might look like this:</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">InvestmentPolicy</span> <span class="tok-attr">xml:lang</span><span class="tok-punct">=</span><span class="tok-string">"en"</span><span class="tok-punct">></span>
The fund invests primarily in large-capitalisation European equities
and uses a <span class="tok-punct"><</span><span class="tok-tag">Benchmark</span><span class="tok-punct">></span>MSCI Europe NR<span class="tok-punct"></</span><span class="tok-tag">Benchmark</span><span class="tok-punct">></span> as its reference.
<span class="tok-punct"></</span><span class="tok-tag">InvestmentPolicy</span><span class="tok-punct">></span>
</code></pre>
<p>When text must contain characters that XML would otherwise interpret — for example, a literal <code><</code> or <code>&</code> — two escape mechanisms are available. The first is the entity-reference mechanism already mentioned (<code>&lt;</code>, <code>&amp;</code>). The second is a <code>CDATA</code> section, which tells the parser "everything inside here is raw text, don't try to interpret it":</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">LegalText</span><span class="tok-punct">></span><span class="tok-decl"><![CDATA[</span><span class="tok-string">
The management fee is 1.25% per annum of the NAV
& is accrued daily.
</span><span class="tok-decl">]]></span><span class="tok-punct"></</span><span class="tok-tag">LegalText</span><span class="tok-punct">></span>
</code></pre>
<p><code>CDATA</code> is most useful when embedding pre-formatted text, such as an HTML fragment or a legal notice, that contains many XML-special characters.</p>
<p>Comments are written <code><!-- like this --></code> and are ignored by parsers. They are invaluable in schemas and in hand-edited sample files, but should not be relied upon to carry information that downstream consumers need, because many XML tool chains discard them silently. Processing instructions of the form <code><?target data?></code> also exist; FundsXML does not use them beyond the XML declaration itself, and a practitioner need only recognise them.</p>
<hr>
<h2>2.4 Character Encoding and the XML Declaration</h2>
<p>The first line of almost every XML file is the <em>XML declaration</em>:</p>
<pre><code><span class="tok-decl"><?xml version="1.0" encoding="UTF-8"?></span>
</code></pre>
<p>Three things are worth knowing about it.</p>
<p>First, the declaration is strictly optional under XML 1.0 when the encoding is UTF-8 or UTF-16, but in practice every serious tool chain emits it. Always include it.</p>
<p>Second, the <code>encoding</code> attribute tells the parser how the bytes in the file map onto characters. UTF-8 is the default in practice and should be the default in your own production of FundsXML files. The alternatives — ISO-8859-1, Windows-1252, UTF-16 — are legacy choices that cause avoidable pain, most commonly when a German umlaut, a French accent, or a non-breaking space survives a round trip through a tool chain that guesses the encoding wrongly.</p>
<p>Third, UTF-8 files may be preceded by a three-byte <em>byte-order mark</em> (the BOM, <code>EF BB BF</code>). Some Windows tools write the BOM by default; some Unix tools refuse to parse a file that begins with it. Neither behaviour is strictly wrong, but the combination is a reliable source of production incidents. The safe rule for FundsXML work is: <strong>emit UTF-8 without a BOM</strong>, and treat the appearance of a BOM in an incoming file as a yellow flag worth investigating.</p>
<p>Encoding is not an academic concern for the fund industry. Multi-lingual fund names, legal disclaimers with em-dashes and typographic quotes, and regulatory text with accented characters all pass through the same pipeline as the numbers. A single mis-configured character set turns <em>Société Générale</em> into <em>Société Générale</em>, and a downstream regulator is unlikely to laugh.</p>
<hr>
<h2>2.5 Namespaces</h2>
<h3>2.5.1 Why namespaces exist</h3>
<p>As soon as XML documents began to combine data from multiple sources, a practical problem emerged. Two independently designed vocabularies might both use an element called <code>Name</code>, or <code>Address</code>, or <code>Type</code>. Without some way of telling them apart, a document that mixed them would be ambiguous.</p>
<p>XML namespaces solve this by giving every element and attribute a two-part name: a namespace URI (which acts as a globally unique identifier) and a local name (the short name used in the document). Two elements share a name only if both parts match.</p>
<h3>2.5.2 Declaring and using namespaces</h3>
<p>A namespace is bound to a prefix (or to the default) by an <code>xmlns</code> attribute:</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">Fund</span> <span class="tok-attr">xmlns</span><span class="tok-punct">=</span><span class="tok-string">"http://example.org/illustrative/fund"</span>
<span class="tok-attr">xmlns:sig</span><span class="tok-punct">=</span><span class="tok-string">"http://www.w3.org/2000/09/xmldsig#"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">Name</span><span class="tok-punct">></span>Europa Growth Fund<span class="tok-punct"></</span><span class="tok-tag">Name</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">sig:Signature</span><span class="tok-punct">></span>
<span class="tok-comment"><!-- digital signature content, treated in Chapter 9 --></span>
<span class="tok-punct"></</span><span class="tok-tag">sig:Signature</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">Fund</span><span class="tok-punct">></span>
</code></pre>
<p>Two namespaces are in play here. The default namespace, declared by <code>xmlns="..."</code> without a prefix, applies to <code><Fund></code> and <code><Name></code>. The second namespace is bound to the prefix <code>sig:</code> and applies to <code><sig:Signature></code>. A consumer that understands both vocabularies can process each subtree independently.</p>
<p>Three points deserve emphasis because they are the source of most namespace-related confusion:</p>
<ul>
<li><strong>The URI is an identifier, not an address.</strong> Nothing lives at <code>http://example.org/illustrative/fund</code>. The URI is chosen for uniqueness, not for retrieval. FundsXML's own namespace URIs follow the same convention.</li>
<li><strong>Prefixes are local aliases, not part of the name.</strong> The same document could write <code>xmlns:f="http://example.org/illustrative/fund"</code> and then use <code><f:Fund></code> instead of <code><Fund></code>; both forms identify the same element. Tools that compare XML must compare the expanded names, not the prefixed ones.</li>
<li><strong>Default namespaces propagate to descendants.</strong> Once a default namespace is declared on an element, every unprefixed descendant element is in that namespace — until an inner element redeclares it. Attributes are not covered by the default namespace; an unprefixed attribute is in no namespace at all. This asymmetry surprises newcomers and is worth remembering.</li>
</ul>
<h3>2.5.3 Namespace-aware tooling</h3>
<p>A recurring field-failure pattern around FundsXML is the use of a tool that is not namespace-aware. Such tools treat <code><f:Fund></code> and <code><Fund></code> as different elements purely on the basis of the textual prefix, and produce XPath queries that silently return empty results against files whose authors happen to have chosen a different prefix. Every tool shown in this book — xmllint, oXygen, IntelliJ, VS Code, and the FreeXmlToolkit treated in Chapter 11 — is namespace-aware. If you ever find yourself writing an XPath expression against a FundsXML document that matches nothing despite an obvious element being present, the first diagnosis should always be: <em>am I missing a namespace binding?</em></p>
<hr>
<h2>2.6 From Well-Formed to Valid: Enter XSD</h2>
<p>Well-formedness asks whether a document obeys XML's syntactic rules. <em>Validity</em> asks a stronger question: does the document obey the rules of some particular vocabulary? Those rules — which elements may appear, in what order, how often, with what types of content, and with what attributes — are written in a <em>schema</em>, and the act of checking a document against that schema is <em>schema validation</em>.</p>
<p>XML has more than one schema language. Three are worth knowing by name:</p>
<ul>
<li><strong>DTD (Document Type Definition)</strong> is the original schema language, inherited from SGML. It is expressive but crude: it has no notion of data types beyond "string", no namespace support worth using, and a syntax that is not itself XML. DTDs survive in legacy corners of publishing and HTML but are a historical curiosity for FundsXML purposes.</li>
<li><strong>Relax NG</strong> is an elegant, pattern-based schema language that is technically superior to XSD in several ways and is used, for example, by OpenDocument. Its weaker tooling support in enterprise environments has limited its adoption in financial standards.</li>
<li><strong>XSD (XML Schema Definition)</strong>, governed by the W3C, is the schema language FundsXML uses. It is itself an XML vocabulary — meaning schemas can be parsed by the same tools that parse instance documents — and it supports a rich type system, namespaces, inheritance, and modularisation.</li>
</ul>
<p>FundsXML chose XSD for pragmatic reasons. XSD is supported by every serious XML tool, every major programming language, and every enterprise integration platform. Its type system is expressive enough to enforce formats such as ISIN, date, and decimal precision, and its modularisation features scale to the dozens of schema files that make up a modern FundsXML release. No other schema language would have been as durable a choice in 2001, and none has meaningfully displaced it in the two decades since.</p>
<p>The rest of this chapter therefore teaches XSD, and only XSD. When the book speaks of "the schema" from Chapter 3 onwards, it means an XSD schema.</p>
<hr>
<h2>2.7 XSD Simple Types</h2>
<p>XSD divides types into two categories. A <em>simple type</em> is a type that constrains a single leaf value — the text content of an element or the value of an attribute. A <em>complex type</em> describes the structure of an element with child elements and attributes. This section treats simple types; §2.8 treats complex types.</p>
<h3>2.7.1 Built-in simple types</h3>
<p>XSD provides several dozen built-in simple types. A fund-industry practitioner needs to recognise the following core set on sight:</p>
<p><strong>Table 2.1 — Core XSD built-in types for fund data</strong></p>
<table>
<thead>
<tr><th>Type</th><th>Purpose</th><th>Example value</th></tr>
</thead>
<tbody>
<tr><td><code>xs:string</code></td><td>Arbitrary text</td><td>Europa Growth Fund</td></tr>
<tr><td><code>xs:normalizedString</code></td><td>Text with whitespace normalised</td><td>Europa Growth Fund</td></tr>
<tr><td><code>xs:token</code></td><td>Text with leading, trailing, and multiple internal whitespace collapsed</td><td>EUR</td></tr>
<tr><td><code>xs:boolean</code></td><td><code>true</code> / <code>false</code> (or <code>1</code> / <code>0</code>)</td><td>true</td></tr>
<tr><td><code>xs:decimal</code></td><td>Arbitrary-precision decimal number</td><td>123.456789</td></tr>
<tr><td><code>xs:integer</code></td><td>Whole number</td><td>42</td></tr>
<tr><td><code>xs:double</code></td><td>64-bit floating point</td><td>1.2345E3</td></tr>
<tr><td><code>xs:date</code></td><td>ISO-8601 date</td><td>2026-04-30</td></tr>
<tr><td><code>xs:dateTime</code></td><td>ISO-8601 date with time and optional timezone</td><td>2026-04-30T17:30:00+02:00</td></tr>
<tr><td><code>xs:gYear</code></td><td>A four-digit year</td><td>2026</td></tr>
<tr><td><code>xs:anyURI</code></td><td>A URI (used for namespace references and links)</td><td>http://example.org/f</td></tr>
<tr><td><code>xs:ID</code> / <code>xs:IDREF</code></td><td>A unique identifier / a reference to one</td><td>EGF-001</td></tr>
</tbody>
</table>
<p>A few observations matter for fund data. <code>xs:decimal</code> is the correct type for monetary values and NAVs: it is arbitrary-precision and does not suffer from the rounding surprises of <code>xs:double</code>. <code>xs:date</code> and <code>xs:dateTime</code> require ISO-8601 format — year-month-day, not the assorted national variants; a pipeline that accepts <code>30/04/2026</code> is accepting something that is not a valid <code>xs:date</code>. <code>xs:boolean</code> accepts <code>true</code>, <code>false</code>, <code>1</code>, and <code>0</code>, and nothing else; values like <code>Y</code> or <code>Yes</code> are invalid.</p>
<h3>2.7.2 Restricting built-in types</h3>
<p>The real power of XSD simple types comes from <em>restrictions</em> (formally called <em>constraining facets</em>): building a new simple type by constraining an existing one. XSD defines twelve constraining facets, and each facet is applicable only to certain families of types. Table 2.2 gives the complete picture.</p>
<p><strong>Table 2.2 — XSD constraining facets at a glance</strong></p>
<table>
<thead>
<tr><th>Facet</th><th>Applies to</th><th>Effect</th></tr>
</thead>
<tbody>
<tr><td><code>enumeration</code></td><td>all types</td><td>Value must be one of a listed set</td></tr>
<tr><td><code>pattern</code></td><td>all types</td><td>Value must match a regular expression</td></tr>
<tr><td><code>whiteSpace</code></td><td>string types</td><td>Controls whitespace handling: <code>preserve</code>, <code>replace</code>, or <code>collapse</code></td></tr>
<tr><td><code>length</code></td><td>string, binary, list types</td><td>Value must have exactly this length</td></tr>
<tr><td><code>minLength</code></td><td>string, binary, list types</td><td>Value must have at least this length</td></tr>
<tr><td><code>maxLength</code></td><td>string, binary, list types</td><td>Value must have at most this length</td></tr>
<tr><td><code>minInclusive</code></td><td>numeric, date/time types</td><td>Value must be ≥ this bound</td></tr>
<tr><td><code>minExclusive</code></td><td>numeric, date/time types</td><td>Value must be > this bound</td></tr>
<tr><td><code>maxInclusive</code></td><td>numeric, date/time types</td><td>Value must be ≤ this bound</td></tr>
<tr><td><code>maxExclusive</code></td><td>numeric, date/time types</td><td>Value must be < this bound</td></tr>
<tr><td><code>totalDigits</code></td><td><code>xs:decimal</code> and derived</td><td>Maximum total number of digits</td></tr>
<tr><td><code>fractionDigits</code></td><td><code>xs:decimal</code> and derived</td><td>Maximum number of fractional digits</td></tr>
</tbody>
</table>
<p>Several facets can be combined in a single restriction — for example, a <code>pattern</code> and a <code>maxLength</code> on the same type. The XSD processor checks every facet; the value must satisfy all of them.</p>
<p>The following worked examples, drawn from Europa Growth Fund data, illustrate each family of facets.</p>
<h4>String restrictions: <code>pattern</code>, <code>length</code>, <code>minLength</code>, <code>maxLength</code></h4>
<p><strong>An ISIN pattern.</strong> An ISIN is exactly twelve characters: two letters (the country code), followed by nine alphanumeric characters, followed by one decimal digit (the check digit). The XSD that expresses this is:</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">xs:simpleType</span> <span class="tok-attr">name</span><span class="tok-punct">=</span><span class="tok-string">"ISINType"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:restriction</span> <span class="tok-attr">base</span><span class="tok-punct">=</span><span class="tok-string">"xs:string"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:pattern</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"[A-Z]{2}[A-Z0-9]{9}[0-9]"</span><span class="tok-punct">/></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:restriction</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:simpleType</span><span class="tok-punct">></span>
</code></pre>
<p>A value of <code>LU0000000001</code> validates; a value of <code>LU000000000</code> (eleven characters) does not, and neither does <code>lu0000000001</code> (lowercase country code). The <code>pattern</code> facet uses the regular-expression syntax defined by XSD, which is similar to — but not identical with — the Perl-style regular expressions most programmers know. The most important differences are that XSD patterns always match the <em>entire</em> value (no need for <code>^</code> and <code>$</code> anchors) and that some shorthand character classes differ.</p>
<p><strong>A bounded text field.</strong> Many FundsXML text fields carry a maximum-length constraint to prevent absurdly long values from reaching the consumer. A typical text field limited to 256 characters:</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">xs:simpleType</span> <span class="tok-attr">name</span><span class="tok-punct">=</span><span class="tok-string">"Text256Type"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:restriction</span> <span class="tok-attr">base</span><span class="tok-punct">=</span><span class="tok-string">"xs:string"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:maxLength</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"256"</span><span class="tok-punct">/></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:restriction</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:simpleType</span><span class="tok-punct">></span>
</code></pre>
<p>For an exact-length field — a two-letter ISO country code, for example — the <code>length</code> facet is more appropriate than the combination of <code>minLength</code> and <code>maxLength</code>:</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">xs:simpleType</span> <span class="tok-attr">name</span><span class="tok-punct">=</span><span class="tok-string">"ISOCountryCodeType"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:restriction</span> <span class="tok-attr">base</span><span class="tok-punct">=</span><span class="tok-string">"xs:string"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:length</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"2"</span><span class="tok-punct">/></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:pattern</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"[A-Z]{2}"</span><span class="tok-punct">/></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:restriction</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:simpleType</span><span class="tok-punct">></span>
</code></pre>
<p>Here <code>length</code> and <code>pattern</code> work together: the value must be exactly two characters <em>and</em> must consist of two uppercase letters. Either facet alone would be insufficient — <code>length</code> alone would accept <code>12</code>, and <code>pattern</code> alone would accept <code>ABC</code> if the expression were written carelessly.</p>
<h4>Enumeration: <code>enumeration</code></h4>
<p><strong>A currency enumeration.</strong> ISO 4217 defines the three-letter alphabetic currency codes. A minimal enumeration covering the currencies in which the Europa Growth Fund issues share classes might be:</p>
<pre><code><span class="tok-punct"><</span><span class="tok-tag">xs:simpleType</span> <span class="tok-attr">name</span><span class="tok-punct">=</span><span class="tok-string">"CurrencyType"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:restriction</span> <span class="tok-attr">base</span><span class="tok-punct">=</span><span class="tok-string">"xs:string"</span><span class="tok-punct">></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:enumeration</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"EUR"</span><span class="tok-punct">/></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:enumeration</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"USD"</span><span class="tok-punct">/></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:enumeration</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"CHF"</span><span class="tok-punct">/></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:enumeration</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"GBP"</span><span class="tok-punct">/></span>
<span class="tok-punct"><</span><span class="tok-tag">xs:enumeration</span> <span class="tok-attr">value</span><span class="tok-punct">=</span><span class="tok-string">"JPY"</span><span class="tok-punct">/></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:restriction</span><span class="tok-punct">></span>
<span class="tok-punct"></</span><span class="tok-tag">xs:simpleType</span><span class="tok-punct">></span>
</code></pre>
<p>In production, the enumeration would cover the complete ISO 4217 list. The principle is the same: an enumeration is the correct way to pin a field to a closed set of values, and it costs nothing at runtime. Enumerations are not limited to strings — they work on any type. An enumeration of <code>xs:integer</code> values, for example, can restrict a field to a fixed set of numeric codes.</p>