第二章節：Document Model 為什麼不會重蹈歷史覆轍？ Nissen

[nissenyeh]

背景

• 文章中有一個段落再談 Are Document Databases Repeating History?（Document Databases在重複歷史嗎）
  • 背景是 hierarchical model 因為遇到資料 duplicate 問題，所以才後面出現 network 與 relational model 的競爭，最後由 relational model 獲勝，但到現在又出現 Document Model ，如果又是同樣的類似於 JSON / tree 結構的儲存，一樣跟 hierarchical model 會遇到資料 duplicate 的問題，因此是一種重蹈覆徹。

Comparison to document databases Document databases reverted back to the hierarchical model in one aspect: storing nested records (one-to-many relationships, like positions, education, and contact_info in Figure 2-1) within their parent record rather than in a separate table.

However, when it comes to representing many-to-one and many-to-many relation- ships, relational and document databases are not fundamentally different: in both cases, the related item is referenced by a unique identifier, which is called a foreign key in the relational model and a document reference in the document model [9]. That identifier is resolved at read time by using a join or follow-up queries. To date, document databases have not followed the path of CODASYL.

那文章的觀點是 Document Databases「不是」在重複歷史，因為：

• 雖然 one-to-many 的關係跟 hierarchical model 一樣記錄在 parent record
• 但是 many-to-one and many-to-many 跟 relational databases 一樣的方式儲存（利用 foreign key 關聯）

問題：

• 但他說的有點抽象，具體來說 Document Model，到底是如何處理 many-to-one and many-to-many 關係？（不太懂他的例子，而且 many-to-one 不就是 one-to-many 嗎=_=）

[jxiu0129]

• DB.json vs 很多 json，但是在 application 層有定義關聯