Introduction to Relational Databases

8 July, 2016

An Introduction to Relational Databases

Dr Meriel PatrickPamela Stanworth

http://creativecommons.org/licenses/by-nc-sa/3.0/

STRUCTURING DATA

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Digital Humanities Summer School -An Introduction to Relational Databases

Structuring data

We all structure the information we work with So we can find what we need, when we need it To facilitate evaluation, comparison, and analysis

Choosing the right structure is important

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Our research could be enhanced by having better ways of storing information, because the way I store my thoughts makes a difference to how I use them when progressing in my thinking.

Philosophy research fellow

The structure you select influences…

The kinds of information you collect How it’s possible to interrogate your data The extent to which you

can take advantage of your computer’s data-handling abilities

How easy it is to share data with others

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Options for structuring and analysing data

Tabular data Spreadsheets

Microsoft Excel Google Sheets OpenOffice Calc

Relational databases Microsoft Access FileMaker Pro MySQL PostgreSQL

Non-tabular data Document-orientated

databases Includes XML databases

RDF triplestores Linked data on the Web

Qualitative data analysis packages

NVivo ATLAS.ti

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When to use a relational database

Your data can be organised in tabular form E.g. information about things that share common properties

You are interested in multiple types of entity And the relationships between them Entities may be concrete or more abstract

You want to identify instances of things that meet certain criteria

You want to be able to present one dataset in multiple different ways Query results can be exported and used elsewhere

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Benefits of relational databases

More accurate representation of complex data And helps avoid duplication of information

Permits flexible querying Wider range of questions possible than with a spreadsheet Useful if you’re unsure which questions you’ll want to ask

Suitable for collaborative use Multiple people can access and use the same database Can encourage (or enforce) consistency in data entry

Technology has been around for several decades Widely supported and well understood

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AN EXAMPLE

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A table of bibliographic data

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A table of bibliographic data

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One author, four different name formats

One name, two authors

We might try to clarify things…

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But this involves lots of repetition


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And may get confusing and

unwieldy

An alternative approach

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Separate table for author details


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Further possible refinements

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Publishers could also be split out into a separate

table


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We could create a standardised

list of types


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We could distinguish different editions of

the same title

The right relational database structure lets us do all this

and more

DESIGNING A DATABASE

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Database terms

A database is a collection of data Data is organised into one or more tables Each row is a record Each column is a field Name Role Town

record 1 Peter farmer Oxford

record 2 Mary weaver Winchester

record 3 Seth drover Bristol

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Decide on the fields

Think of all the facts that will be collected

plenty of fields consult widely small facts, “atomic” difficult to add later

Designing the tables

Plan it on paper first Choose the fields, then group them in tables

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Designing the tables

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PeopleSurname Wilson Temple Sterling Elliott

First name Adam Thos Oliver Justin

Middle initial(s) T G J K W

Date of birth 3/8/1697 6/10/1705 23/5/1720 24/2/1718

…Notes Born France London landowner

Types of data

Set a data type for each field:

Text, Number, Date/time, Currency, Yes/No

PeopleSurname text

First name text

Middle initial(s) text

Date of birth date

…

Notes memo

BooksTitle text

Author text

DatePub date

…

Place text

ISBN text

…

…

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An example scenario

Study of 18th century book trade

What things are we interested in?

Publications

Publishers

People

And possibly our sources for the information we’re collecting

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An example scenario

And what information might we want to know about each of these things?

Names

Dates

Places

Where we got the information from

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Person

Surname

First name

Middle initial(s)

Date of birth

Notes

Publication

Title

Author(s)

Publisher

Date of publication

Place of publication

Edition

Format

Type of publication

Price

Sales

Notes

Publisher

Name

Staff

Founded

Ceased

Address

Notes

Reference

Author(s)

Title

Date of publication

Edition

Volume

Page(s)

URL

Notes

JOINS BETWEEN TABLES

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Primary key

Each table needs a primary key Choose (at least) one field that only contains

unique values Commonly an auto-incrementing whole (integer) number

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Person

PersonID

Surname

First name

Middle initial(s)

Date of birth

Notes

Publication

PubnID

Title

Author(s)

Publisher

Date of publication


Edition

Format

Type of publication

Price

Sales

Notes

Publisher

PublisherID

Name

Staff

Founded

Ceased

Address

Notes

Reference

ReferenceID

Author(s)

Title

Date of publication

Edition

Volume

Page(s)

URL

Notes

Relating two tables - joins

Mark the field that links this table to that table Draw join lines Convenient to have same or similar field names

Person

PersonID

Surname

First name

Middle initial(s)

Date of birth

Notes

Reference

PageInReference

Publication

PubnID

Title

Author

Publisher

Date of publication


Edition

Format

Type of publication

Price

Reference

PageInReference

Publisher

PublisherID

Name

Staff

Founded

Ceased

Address

Reference

PageInReference

Reference

ReferenceID

Author(s)

Title

Date of publication

Edition

Volume

Page(s)

URL

Notes


1

∞

1

∞

∞

∞

Publication

PubnID

Title

Author(s)

Publisher

Date of publication


Edition

Format

Type of publication

Price

Reference

PageInReference


∞

1

1

Person

PersonID

Surname

First name

Middle initial(s)

Date of birth

Notes

Reference

PageInReference

Publisher

PublisherID

Name

Staff

Founded

Ceased

Address

Reference

PageInReference

Reference

ReferenceID

Author(s)

Title

Date of publication

Edition

Volume

Page(s)

URL

Notes

1

∞

1

∞

∞

∞

Many to many

Authorship

ID

Author

Publication∞

Publication

ID Int

Title Text

Publisher INT

Date of publication

Int?


Text

Edition Int

Format Text

Type of publication

Text

Price Dec?

Sales Int?

Reference Int

Page Text

Notes Text

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Person

AuthorID Int

Surname Text

First name Text

Middle initial(s)

Text

Date of birth Date

Reference Int

Page Text

Notes Text

Publisher

ID Int

Name Text

Founded Int?

Ceased Int?

Address Text

Reference Int

Page Text

Notes Text

Reference

ID Int

Title Text

Date of publication

Int?

Edition Int?

Volume Int?

URL Text

Notes Text

1

∞?

1

∞

∞

∞

Man

y to

man

y

Publisher_Staff

ID Int

Publisher Int

Staff_Member Int

Reference_Author

ID Int

Reference Int

Reference_Author Int

∞

∞

1

1

∞

∞

∞

∞

Authorship

ID Int

Author Int

Publication Int

A USER-FRIENDLY DATABASE

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Easiest for people to work on datausing forms Too risky to work on data in tables

A form or view is safe and efficient for humans Typically one record at a time Easy to use Related data appears

via drop-downs

Database design: A workflow

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WHAT NEXT?

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Once you’ve created your database…

Ask questions by constructing queries Find the records that meet certain criteria Search, sort, count, and filter data Perform basic mathematical and statistical operations

Export data for other types of analysis Share your results with others

Some packages produce nicely formatted reports

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Query results

Results may resemble another table or spreadsheet But the contents are customised to your requirements

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8 July, 2016

What kind of questions could you ask?

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How many titles did publisher x publish between 1750 and 1759? How does this compare with other decades?

Who both authored and published books? Did they write and publish in the same genre?

Were first editions of works by author y typically published in quarto or octavo formats?

Were later editions typically cheaper than earlier ones?

What kind of questions could you ask?

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How did author z’s popularity vary through the century (as measured by the intervals between new editions)?

If one publisher ceased operations, did their staff tend to switch en masse to another?

Where on earth did I find this bit of information?

Database challenges in the humanities

Patchy or incomplete data Be aware of the difference between 0 and null

Interpreted and uncertain information Fields can indicate the degree of certainty of a

particular ‘fact’ – e.g. definite, probable, or possible Inconsistent or changing terminology

Alternative spellings, different forms of address, name changes

May help to have controlled vocabulary tables

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Database challenges in the humanities

Varying degrees of accuracy Often an issue with historical dates May help to split elements of a date into separate

fields Fuzziness vs. queryableness

There’s often a trade off A format such as ‘c. 310 BCE’ may be more accurate But much harder to search and sort

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NOW YOU TRY IT …

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Your exercise today… Draft a structure for a relational database

recording information about membership of gentlemen’s clubs in Victorian London

Think about the fields, tables, and relationships you’d need

You have a collection of evidence about which clubs people belonged to, and when

However, the information is patchy and not always consistent


Our example solution


Possible enhancements Integer may not be the best data type for uncertain dates Make the relationship between club_memberships and

evidence many-to-many rather than one-to-many Done by adding a link table

Split author entries into a separate table Allows multiple authors for each piece of evidence

Impose a controlled vocabulary on the occupation field by adding a look-up table

Add longitude and latitude to the addresses table


Questions?

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Education

Introduction to Relational Databases