Answers to review questions in "Beginning XSLT": Chapt

Dear all,
This will probably be the last chapter I'll do for a while.  My purpose in
going through "Beginning XSLT" has been to get a solid enough foundation in
XSLT to use it for a project (for my MA thesis).  I feel confident enough now
to turn attention to the project, coming back to this book and others
when needed.  Many thanks to everyone on this list who has helped me get up
to speed by answering my questions and others'!
Thanks too to Kay and Tennison for their excellent books.  And Jeni for
individualized tutoring.

Lars


1. What is the advantage of using ID attributes and the id() function
   over using predicates to search for elements?

Answer: efficiency.


2. What format can the values of ID attributes take?

Answer:
They have to be XML Names, which means they must start with a letter,
underscore, or colon, and contain only "alphanumeric" characters (which
include '.' | '-' | '_' | ':' plus other similar punctuation in Unicode).
In particular, no spaces are allowed.


3. Create an ATTLIST declaration to make the required custNo attribute
   of the <Customer> element an ID attribute.

Answer:
<!DOCTYPE foo [
<!ELEMENT Customer (ANY)>
<!ATTLIST Customer custNo ID #REQUIRED>
]>


4. What three types of arguments can the id() function take and what
   does it return from each?

Answer:
id() can take a string containing a single ID, in which case it returns
the element that has that ID.
id() can take a string containing multiple IDs separated by space, in
which case it returns a node set consisting of the elements that have
those IDs.
id() can take a node set, in which case id() returns a node set
consisting of the elements whose IDs are the values of nodes in the
argument node set.


5. What advantages are there for using keys rather than IDs?

Answer:
a. You're not dependent on an external or internal DTD to declare
   attributes as type ID.
b. You can key on other values than just attributes, sometimes complex ones.
c. Key values can have unrestricted format.
d. You can have different key spaces for different kinds of elements,
   making indices more efficient and making it easier to come up with unique
   key values within a key space.
e. Multiple elements can have the same key value if desired, and each element
   can have several key values.


6. In what situations might you us the keys defined as follows?

Answers:

<xsl:key name="films" match="Film" use="@id" />
When you have a number of <Film> elements that you want to access by their @id
attribute.

<xsl:key name="filmsByCharacters" match="Film"
	 use="CastList/CastMember/Character/Name" />
When you want to group the films by the name of a character in the cast.
Maybe you want to list the characters one by one, and under each character,
list the films they're in.
This is a many-to-many key.

<xsl:key name="filmsByYear" match="Film" use="Year" />
When you want to group the films by the year in which they were made
(the value of the <Year> element child of <Film>).
Perhaps the purpose is to list all films made in 1970, then all those
made in 1971, etc.
This is a one-to-many key.

<xsl:key name="filmsByDirector" match="Film" use="Director/Name" />
When you want to group the films by the name of the director
(the value of the <Name> element child of the <Director> element
child[ren] of <Film>).
This could be a many-to-many key, in the case of multiple directors
per film; or just one-to-many.

<xsl:key name="filmsByYearAndDirector" match="Film"
	 use="concat(Year, ':', Director/Name)" />
When you want to group the films by both year and director.
In conjunction with one of the previous two keys, you could use this
to list films first by year, then within that by director; or vice versa.


7. Construct a stylesheet that groups <Film> elements by their <Year>
   children and by their rating attributes.

Answer:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                version="1.0">

  <xsl:key name="FilmsByYear" match="Film" use="Year" />
  <xsl:key name="FilmsByRating" match="Film" use="@rating" />

  <xsl:template match="/">
    <html>
      <head>
        <style>
          .filmname {
             font-style: italic
          }
        </style>
      </head>
      <body>
        <h1>Films, by Year</h1>
        <xsl:apply-templates select="Films/Film[generate-id() =
                                     generate-id(key('FilmsByYear', Year)[1])]"
                             mode="YearList">
          <xsl:sort select="Year" data-type="number"/>
        </xsl:apply-templates>

        <h1>Films, by Rating</h1>
        <xsl:apply-templates select="Films/Film[generate-id() =
                                     generate-id(key('FilmsByRating', @rating)[1])]"
                             mode="RatingList">
          <xsl:sort select="@rating" order="descending" data-type="number" />
        </xsl:apply-templates>
      </body>
    </html>
  </xsl:template>

  <xsl:template match="Film" mode="YearList">
    <h2><xsl:value-of select="Year" /></h2>
    <xsl:apply-templates select="key('FilmsByYear', Year)" mode="Detail">
      <xsl:sort select="@rating" data-type="number" order="descending" />
    </xsl:apply-templates>
  </xsl:template>

  <xsl:template match="Film" mode="RatingList">
    <h2><xsl:value-of select="@rating" /> stars</h2>
    <xsl:apply-templates select="key('FilmsByRating', @rating)" mode="Detail">
      <xsl:sort select="Year" data-type="number" />
    </xsl:apply-templates>
  </xsl:template>

  <xsl:template match="Film" mode="Detail">
    <p>
      <span class="filmname"><xsl:value-of select="Name" /></span>, 
      <xsl:value-of select="Year" />.  Stars:
      <xsl:value-of select="@rating" />
    </p>
  </xsl:template>

</xsl:stylesheet>


Test data:

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="Review7.xsl"?>

<!-- These ratings and years mostly have nothing to do with reality.
     It's just test data. -->

<Films>
  <Film rating="3">
    <Name>Revenge of the Killer Tomatoes</Name>
    <Year>1962</Year>
  </Film>
  <Film rating="5">
    <Name>Crouching Tiger, Hidden Dragon</Name>
    <Year>2001</Year>
  </Film>
  <Film rating="4">
    <Name>Chicken Run</Name>
    <Year>2000</Year>
  </Film>
  <Film rating="3">
    <Name>Gone with the Cloud</Name>
    <Year>1999</Year>
  </Film>
  <Film rating="4">
    <Name>Woman Reporter</Name>
    <Year>1999</Year>
  </Film>
  <Film rating="5">
    <Name>Long Way from Home</Name>
    <Year>2000</Year>
  </Film>
  <Film rating="3">
    <Name>The Unforgettable Character</Name>
    <Year>1999</Year>
  </Film>
  <Film rating="3">
    <Name>Evergreen Tree</Name>
    <Year>2001</Year>
  </Film>
  <Film rating="4">
    <Name>Orchid in the Rain</Name>
    <Year>2001</Year>
  </Film>
  <Film rating="5">
    <Name>Hour of the Wolf</Name>
    <Year>2000</Year>
  </Film>
  <Film rating="4">
    <Name>Seven Foxes</Name>
    <Year>1999</Year>
  </Film>
</Films>


Lars Huttar
MA student at Graduate Institute for Applied Linguistics, www.gial.edu
web page: http://www.cs.oberlin.edu/~huttar/home.html

	Blind unbelief is sure to err,
	and scan his work in vain;
	God is his own interpreter,
	and he will make it plain. 

		William Cowper, 1774


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