complexType : extension of a sequence by a choice ?

Hi,

I have some questions about extension of complexTypes (and do not found the answer
in the specifications) :

Is extension of a complexType composed of sequence, by using choise is allowed ?
Is extension of a complexType composed of choice, by using sequence is allowed ?

Are these derivations allowed ?

<xs:complexType name="tseq">
    <xs:sequence>
        <xs:element name="t1"/>
        <xs:element name="t2"/>
    </xs:sequence>
</xs:complexType>

<xs:complexType name="tchoi">
    <xs:sequence>
        <xs:element name="t3"/>
        <xs:element name="t4"/>
    </xs:sequence>
</xs:complexType>

<xs:complexType name="tseq-ext-choi">
    <xs:complexContent>
        <xs:extension base="tseq">
            <xs:choice>
                <xs:element name="t3"/>
            </xs:choice>
        </xs:extension>
    </xs:complexContent>
</xs:complexType>

<xs:complexType name="tchoi-ext-seq">
    <xs:complexContent>
        <xs:extension base="tchoi">
            <xs:sequence>
                <xs:element name="t1"/>
            </xs:sequence>
        </xs:extension>
    </xs:complexContent>
</xs:complexType>


If yes, what is the effective content model for these ?

thanks in adance

-- bruno -- 
Bruno Chatel
Tel : (+33) (0)4 96 11 14 57
bcha@chadocs.com
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Received on Wednesday, 4 February 2004 11:42:44 UTC