PhD Defence • Data Systems • Update-Aware Information Extraction

Please note: This PhD defence will take place in DC 2310.

Besat Kassaie, PhD candidate
David R. Cheriton School of Computer Science

Supervisor: Professor Frank Tompa

Information extraction programs (extractors) can be applied to documents to isolate structured versions of some content by creating tabular records corresponding to facts found in the documents. When extracted relations or source documents are updated, we wish to ensure that those changes are propagated correctly. That is, we recommend that extracted relations be treated as materialized views over the document database.

Because extraction is expensive, maintaining extracted relations in the presence of frequent document updates comes at a high execution cost. We propose a practical framework to effectively update extracted views to represent the most recent version of documents.

Our approach entails conducting static analyses of extraction and update programs within a framework compatible with SystemT, a renowned extraction framework based on regular expressions. We describe a multi-level verification process aimed at efficiently identifying document updates for which we can autonomously compute the updated extracted views. Through comprehensive experimentation, we demonstrate the effectiveness of our approach within real-world extraction scenarios.

For the reverse problem, we need to translate updates on extracted views into corresponding document updates. We rely on a translation  mechanism that is based on value substitution in the source documents. We classify extractors amenable to value substitution as stable extractors. We again leverage static analyses of extraction programs to study stability for extractors expressed in a significant subset of JAPE, another rule-based extraction language. Using a document spanner representation of the JAPE program, we identify four sufficient properties for being able to translate updates back to the documents and use them to verify whether an input JAPE program is stable.