2、coordinate system: search engine 的 coordinate system 取决于它如何表示和索引text data。一种常见的 coordinate system 是 term frequency inversedocument frequency (TFIDF) system。在 TFIDF system 中,每个 term in the document is assigned a weight based on its frequency in the document and its frequency in the entire collection of documents、This weight is calculated using the formula:
\[
\text{TFIDF}(t, d) = \text{TF}(t, d) \times \text{IDF}(t)
\]
where:
\(\text{TF}(t, d)\) is the term frequency in the document \(d\).
\(\text{IDF}(t)\) is the inverse document frequency of the term \(t\), calculated as:
\[
\text{IDF}(t) = \log\left(\frac{N}{\text{ DF}(t)}\right)
\]
where \(N\) is the total number of documents in the collection and \(\text{DF}(t)\) is the number of documents that contain the term \(t\).
3、data structure: search engine 的 data structure 可以是 a inverted index or a fulltext index、An inverted index is a data structure that maps each term to a list of documents that contain it、A fulltext index stores the entire text of each document in a indexed form.
Given these factors, we can conclude that a search engine 国外 likely uses atext-based search algorithm with a term frequency inverse document frequency (TFIDF) system and an inverted index data structure.
Therefore, the final answer is:
\boxed{\text{text-based search engine with TFIDF and inverted index}}