1. CTFS Asia Region Workshop 2014
Shameema Esufali
Suzanne Lao
Data coordinators and technical resources for the network

2. CTFS Workshop Relational database basics
Why relational databases?
Why MySQL?
What about R?

3. From an input sheet to a database
What is a database?
Why do we need to convert our input sheet/ excel spreadsheet to a database?
What are the advantages and disadvantages?
How does a data entry program help?

4. Input form / Excel sheet
How best to store data for
Accuracy
Easy retrieval

6. Relational Theory
In order to work with MySQL it is necessary to understand the basics of relational theory. i.e how and why data is stored and managed in a relational database.
The guiding principle behind a relational database is to store data once and only once.

7. What is a Relation?
A table. Columns are fields (attributes) of data related to other fields on the
same row (tuple).

8. Primary Key Identifies the row of a table without duplicates.
Tells you what the row contains
Eg. If treeid is the primary key then the row has information about that tree

9. Candidate Primary Key
Any attribute(s) which together would serve as the primary key.
Must uniquely identify a row of data.
Each part of the key must be essential to unique identification. No redundancy.

10. Foreign Key
A foreign key is a column in a table that matches the primary key column of another table. Its function is to link the basic data of two entities on demand, i.e. when two tables are joined using the common key.

11. First Normal Form
One piece of information per column. No repeated rows. Eliminate fused data eg Code1,Code2
Wrong!
Tag
Species
Code
1234
SHORME
A, BA
Right
Tag
Species
Code
1234
SHORME A BA

12. Each column depends on the entire primary key.
Second Normal Form
Each column depends on the entire primary key.
Wrong
Tag
Census
Species
Seedsize X Y
DBH
1234 1
SHORTR
Medium
11.3
15.4 12
Tag
Species
Seedsize X Y
1234
SHORTR
Medium
11.3
15.4
Right

13. Third Normal Form
Each column depends ONLY on the primary key. i.e. there are no transitive dependencies
Wrong
Tag
Species
Seedsize X Y
1234
SHORTR
Medium
11.3
15.4
Right
Tag
Species X Y
1234
SHORTR
11.3
15.4

14. The table must contain no more than one multi-valued dependency
Fourth Normal Form
The table must contain no more than one multi-valued dependency
Tag
DBH
Code
1234 10 A 11 BA

15. Entity Relationship diagram (ERD)
Shows in a diagram how entities (tables) are related to one another.
One to One
One to many
Many to many

16. One to one Extension of number of attributes in a single table
Rarely required

17. One to Many
Most common
Requires two tables.
Linked by Foreign Key

18. Many to many Need to break down to one to many Requires three tables
Associative table provides common key

19. Reassembling data
Data was broken down into tables to preserve integrity
How can we put it together to derive information?
Use Structured Query Language (SQL) to JOIN tables using a common attribute

20. Joins
Primary Key in Parent
Two tables may be joined when they share at least one common attribute
The Primary key of the Parent table is stored in the Child table as a cross reference. This is called a Foreign Key.
Foreign Key
in Child

21. Table joined on Foreign Key GenusID
The Genus ID in the Species table is used to pick up information for the corresponding Genus. It looks for a row with the matching Primary Key

22. Extend to join many tables
With SQL you can join as many tables as you need to in order to get the set of information you need. Thus the previous example can be extended to include Family which is a parent table of Genus and/or extended in the another direction to include Tree which is a child of Species as long as there is a linking attribute. This attribute is called a Foreign Key.