Levels of Abstraction

Level 1 Tag Structure

<  ts name="the growing book on data structures and algorithms">
      < ts1 name="chap1" keywords="b-tree" URL="xxx/c1" type="mixed">
     < /ts1>
     < ts2 name="chap2" keywords="dynamic hashing" URL="xxx/c2" type="mixed">
     < /ts2>
< /ts>

Level 2 Tag Structure

<  ts name="the growing book on data structures and algorithms">
      < ts1 name="chap1" keywords="b-tree" URL="xxx/c1" type="mixed">
        < ts11  name="sec1" URL="xxx/c1/s1" > < /ts11>
        < ts12  name="sec2" URL="xxx/c1/s2" >
        < /ts12>
     < /ts1>
     < ts2 name="chap2" keywords="dynamic hashing" URL="xxx/c2" type="mixed">
       < ts21  name="sec1" URL="xxx/c2/s1" >
       < /ts21>
     < /ts2>
< /ts>