下面片段是我在一篇SIGMOD文章中看到的、关于倒排表索引（inverted list）的描 述。 请对照评价一下Lucene目前的版本。 我提问的原因是，根据我们的讨论，Lucene当前版本似乎就不是Matrix存储，是什么存 储？ Conceptually, an inverted list is a two-dimensional table, where the i-th row represents indexed keyword Ki and the j-th column represents instance Ij . The cell at the i-th row and j-th column, denoted (Ki, Ij), records the number of occurrences, called occurrence count, of keyword Ki in the attributes of instance Ij . If the cell (Ki,Ij) is not zero, we say instance Ij is indexed on Ki. The keywords are ordered in alphabetic order, and the instances are ordered by their identifiers. Table 1 shows the inverted list for our example triple base. …(这里省略一小段无关文字) In practice, an inverted list is seldom stored as a matrix. There are multiple ways to store an inverted list, such as a sorted array, a prefix B-tree or a Patricia trie. In addition,  describes techniques for compression of inverted lists. The extensions we describe are orthogonal to these physical implementations.