XML-DTD help/clarification needed

Question

I've written the following DTDs for the XML file below. After checking it says it's valid, however, I'm a bit concerned since this is my very first DTD and I'm not sure if it's actually valid or not. Can someone tell me if it's correct? Thanks!

DTD file:

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE articles [
 <!ELEMENT articles (article+)>
 <!ELEMENT article (authors+,journal+)>
 <!ELEMENT authors (author+)>
 <!ELEMENT author (#PCDATA)>
 <!ELEMENT journal (name+, volume?,issue?,published+,url?,pages?)>
 <!ELEMENT name (#PCDATA)>
 <!ELEMENT issue (#PCDATA)>
 <!ELEMENT published (#PCDATA)>
 <!ELEMENT volume (#PCDATA)>
 <!ELEMENT pages (#PCDATA)>
 <!ELEMENT url (#PCDATA)>

 <!ATTLIST article title CDATA #REQUIRED id ID #REQUIRED>
 <!ATTLIST pages start CDATA #REQUIRED end CDATA #REQUIRED>
 <!ATTLIST url href CDATA #REQUIRED>

 ]>

XML File:

 <articles>
<article title="Computing" id="a1">
    <authors>
        <author>Fhilbertie</author>
        <author>Alicen</author>
        <author>PeDra</author>
    </authors>
    <journal>
        <name>Journals</name>
        <volume>5</volume>
        <issue>6</issue>
        <published>06/11/2013</published>
        <pages start="52" end="79"/>
    </journal>
</article>

<article title="Instruction Sets: Free Will?" id="a2">
    <authors>
        <author>Sallie</author>
        <author>Philber</author>
    </authors>
    <journal>
        <name>Metaphysics</name>
        <volume>5</volume>
        <issue>6</issue>
        <published>06/26/2015</published>
        <pages start="366" end="366"/>
    </journal>
</article>

<article title="My Journy" id="a3">
    <authors>
        <author>Lawrence</author>
    </authors>
    <journal>
        <name>M Magic</name>
        <volume>6</volume>
        <issue>4</issue>
        <published>11/12/1988</published>
    </journal>
</article>

<article title="RDF Triples and the Path to Human Subjugation" id="a4">
    <authors>
        <author>Allison Peony</author>
        <author>Robert Zephyr</author>
        <author>Sally Piper</author>
    </authors>
    <journal>
        <name>Journal of Nefarious Artificial Intelligence</name>
        <published>05/25/2006</published>
        <url href="http://example.com/rdf-triples-subjugation"/>
    </journal>
</article>

<article title="Marksideways, a Markdown Alternative" id="a5">
    <authors>
        <author>Gerald Quinoa</author>
        <author>P. von Cookie</author>
    </authors>
    <journal>
        <name>Marvelous Markup Magic</name>
        <volume>13</volume>
        <issue>3</issue>
        <published>03/14/2013</published>
        <url href="http://example.com/marksidways"/>
    </journal>
</article>

<article title="Hills" id="a6">
    <authors>
        <author>Robert Z</author>
        <author>Leonard P</author>
    </authors>
    <journal>
        <name>Journal Intelligence</name>
        <published>05/25/2014</published>
        <url href="http://example.com/hill"/>
    </journal>
</article>

Answer 1

I've checked the DTD and the XML. Looks quite fine for me, at least syntactically. (This is the answer to your question.)

Few hints:

• If you want an elaborate review, consider posting it on the https://codereview.stackexchange.com/ (make sure you read and comply to the rules there).
• Why DTD? Quite outdated, consider using an XML Schema.
• Search for other schemas in this area. BibTeXML is one of the things I heard of, but there must be tons of them. Check what big resources use.