Interview Bank

RAG in 14 Days: From Retrieval to Trustworthy Answers

D3 Getting Documents In: Parsing PDF and HTML, Tables and Scans, Cleaning Rules, and Metadata You Must Keep

• Which metadata should a document parsing stage preserve, and which downstream feature breaks if you drop each one?文档解析阶段应该保留哪些元数据？少了其中某一项会在哪个环节出问题？

  Common in ChinaCommon overseasIntermediate#metadata#ingestion#access-control

  How to reason about it · think before answering

  1. The trap here is answering with a bare list. The differentiator is pairing every field with a concrete downstream feature. Listing eight fields without naming who consumes them shows you never designed one.
  2. Give the selection rule first: can this be recovered from the original file later? If not, it must be captured at parse time. Formatting and whitespace can be dropped because the original still has them.
  3. Then map fields to consumers: a stable chunk id makes citations verifiable, a heading path tells the user which section a sentence came from and enables structure-aware chunking, page numbers make citations land on the right page, an access-control label enables filtering inside retrieval, an updated-at date resolves conflicting sources, and a content hash enables incremental sync.
  4. Take two of them all the way to cost. Without the access label you must re-parse the whole corpus when access control lands, and worse, people work around it by filtering at generation time, which means the content already reached the context and the leak already happened.
  5. Without a content hash, every sync is a full rebuild: re-parse, re-chunk, re-embed. For a few thousand documents synced daily, the embedding bill alone settles the argument.
  6. Expected follow-up: what about a field you are unsure of? Be conservative. Storage is the cheapest part of the pipeline, and adding a field costs far less than re-running a full parse.

  分析过程 · 先想清楚再作答

  1. 这题最容易答成列清单。区分度不在你能列出几个字段，而在能不能给每个字段配一个具体的下游功能——列了八个字段却说不出谁在用，等于没设计过。
  2. 用一条判据把字段选出来：删掉之后还能不能从原件重新恢复。不能恢复的，解析时就必须留；能恢复的（比如格式、空白）可以放心丢。
  3. 然后一一对应地说：块编号支撑可验证的引用，没有它引用就只能靠模型自觉；标题路径支撑「这句话出自哪一节」和按结构切块；页码支撑引用精确到页；权限标签支撑检索层过滤；更新时间支撑材料冲突时的取舍；内容指纹支撑增量同步。
  4. 挑两个讲透代价。权限标签少了，等到要做访问控制时只能全量重新解析一遍；更糟的是有人会图省事在生成阶段过滤，那等于内容已经进了上下文，泄露已经发生。
  5. 内容指纹少了，每次同步都是全量重建：重新解析、重新切块、重新向量化。一份几千篇的知识库每天重算一次，光 embedding 的账单就够说服任何人。
  6. 可预期的追问：字段拿不准要不要留怎么办？答保守——存储是整条链路上最便宜的一环，加一个字段的代价远小于重跑一次全量解析。

  Key points

  • The rule is recoverability: if it cannot be recovered from the original later, capture it at parse time.
  • Chunk ids back verifiable citations, heading paths back localisation and structure-aware chunking, page numbers make citations land precisely.
  • Access-control labels must be attached during parsing, otherwise enabling ACL means re-parsing everything, and teams end up filtering at generation time where the leak has already occurred.
  • Updated-at lets you present conflicting sources side by side; a content hash enables incremental sync instead of full rebuilds.
  • When unsure, keep the field: storage is far cheaper than a full re-parse.

  答题要点

  • 判据是「删了还能不能从原件恢复」，不能恢复的必须在解析时留下。
  • 块编号服务于可验证的引用，标题路径服务于定位与按结构切块，页码服务于引用精确到页。
  • 权限标签必须在解析时打上，否则做访问控制时要全量重解析，且容易被错误地放到生成阶段过滤。
  • 更新时间用于材料冲突时并列两种说法，内容指纹用于增量同步，少了它每次都要全量重建。
  • 拿不准就保守保留：加一个字段的成本远低于重跑一次全量解析。