<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://www.crossref.org/clinicaltrials.xsd"
    xmlns="http://www.crossref.org/clinicaltrials.xsd">

    <xsd:annotation>
        <xsd:documentation>  
         Linked Clinical Trials is a CrossRef initiative helping to connect the published literature to registered clinical trials associated with the research,
         
            - version 1.0 (initial release) September 24, 2015
        </xsd:documentation>
    </xsd:annotation>

    <xsd:element name="program">
        <xsd:annotation>
            <xsd:documentation>Accommodates deposit of linked clincal trials metadata. The clinical-trial-number value will
                be a string that must match a specific pattern appropriate for a given clinical trial registry. The
                registry is identified in the required attribute 'registry' and must be the DOI of a recognized registry
                (see http://dx.doi.org/10.18810/registries)
            </xsd:documentation>
        </xsd:annotation>
        
        <xsd:complexType>
            <xsd:sequence>
                <xsd:element ref="clinical-trial-number" minOccurs="0" maxOccurs="unbounded"/>
            </xsd:sequence>
        </xsd:complexType>
    </xsd:element>

    <xsd:element name="clinical-trial-number">
        <xsd:complexType mixed="true">
            <xsd:attribute name="registry" use="required">
                <xsd:annotation>
                    <xsd:documentation> The clinical trial identifier related to the article.
                    </xsd:documentation>
                </xsd:annotation>
                <xsd:simpleType>
                    <xsd:restriction base="xsd:string">
                        <xsd:maxLength value="200"/>
                        <xsd:minLength value="12"/>
                        <xsd:pattern value="10.18810/[a-z-]+"/>
                    </xsd:restriction>
                </xsd:simpleType>
            </xsd:attribute>
            <xsd:attribute name="type" use="optional">
                <xsd:annotation>
                    <xsd:documentation> Used to identify the article publication date in relation to the issuance of the trial results
                    </xsd:documentation>
                </xsd:annotation>
                <xsd:simpleType>
                    <xsd:restriction base="xsd:string">
                        <xsd:enumeration value="preResults"/>
                        <xsd:enumeration value="results"/>
                        <xsd:enumeration value="postResults"/>
                    </xsd:restriction>
                </xsd:simpleType>
            </xsd:attribute>
        </xsd:complexType>
    </xsd:element>

</xsd:schema>
