Characteristics of Semi-Structured Data

structure is irregular: missing or additional attributes (labels)
parts of data lack structure, e.g., images
some may yield little structure, e.g., plain text
a-priori schema vs a-posteriori dataguide
- db: fix the schema, then populate the db
- web: design pages, then design schema to facilitate access
schema is large
schema is often ignored, e.g., information retrieval queries
schema is rapidly evolving