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XML work - PART 1 One way to represent a relational...

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PART 1 One way to represent a relational database table as an XML document is to allow the document element to represent the table itself, and each row (tuple) inside the table to be represented by a nested element. Inside the tuple-elements, each column is in turn represented by a nested element. Columns that allow null values are represented by optional elements, and a missing element denotes a null value. Consider the following three table schemas: SAILORS(Sid, Sname, Rating, Age) BOATS(Bid, Bname, Color, Price) RESERVES(Sid, Bid, Date) We can use three separate documents named sailors.xml , boats.xml , and reserves.xml with the following DTDs to represent the above three tables: <!DOCTYPE sailors [ <!ELEMENT sailors (sailor_tuple*)> <!ELEMENT sailor_tuple (sid, sname, rating?, age)> <!ELEMENT sid (#PCDATA)> <!ELEMENT sname (#PCDATA)> <!ELEMENT rating (#PCDATA)> <!ELEMENT age (#PCDATA)> ]> <!DOCTYPE boats [ <!ELEMENT boats (boat_tuple*)> <!ELEMENT boat_tuple (bid, bname, color, price> <!ELEMENT bid (#PCDATA)> <!ELEMENT bname (#PCDATA)> <!ELEMENT color (#PCDATA)> <!ELEMENT price (#PCDATA)> ]> <!DOCTYPE reserves [
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