Design a Database Schema to Store Metadata

1
Design a Database Schema to Store Metadata
2
The Target of Database

• Database is used to store data.
• What is data?
• The description of concrete things (a student, a
  book)
• The description of abstract things (relationship)
• Database schema
• Store the description of the stored data
• Metadata of the stored data

3
Metadata

• The description? of data
• What is these descriptions?
• A physical description
• The height of a student
• The price of a book
• A relation description
• The book belongs to Mike.
• Etc.

4
Example
Metadata of a book
Two copies
5
Example

• How to record the relation of the two copies and
  the metadata?

• Not Good!
• waste storage
• While the metadata changes, 2 record-fields have
  to be updated.

• Better!
• Can clearly find the relation
• Less storage space and less update overhead.

6
Example
Many subjects
7
Example

• How to record the subjects in the metadata?

• Not Good!
• We do not know the max. of subject.

• Better!
• No limitation of the of subjects

8
Example
9
Example

• How to record the common-values in the metadata?

• Not Good!
• Storage space wastes.
• Update overhead

Better!
10
Example

• Actually, we can store the whole metadata in a
  metadata table.
• It is not a good solution, because of the
  efficiency, storage space, etc.
• Do not store the data which related to metadata,
  such as the data of copies, in the metadata
  table.
• In metadata, if there are some multi-value
  fields, separate these from the metadata table.
• Separate the common-value (ex. ??????) from the
  metadata table.
• Only keep the single-value, single-field, and
  non-common-value data in the metadata table.