Meta is a prefix which means “information about” something or “description about” something. For example meta-analysis means information about analysis. Meta-language means information about language. In same way the information about data is called metadata.
Where is metadata?
Metadata is everywhere in our computer’s life. Most of us work with metadata everyday but some people don’t know that they are interacting with it.
A very simple example of metadata is xml file. Look at this example, this xml file contains information about data (person), this information consists of person’s id, name of this person, company and designation etc.
<person> <userID>1234</userID> <firstName>Khan</firstName> <lastName>Abid</lastName> <company>ABC Corp</company> <title>Product Manager</title> <emailAddress>email@example.com</emailAddress> <phone>000-111-555</phone> </person>
Check another example, mobile developers are familiar with this xml
<Button> android:id="@+id/btnOK" android:layout_width="wrap_content" android:layout_marginTop="8dp" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:text="OK" </Button>
This metadata contains information about Button object: what is the id of this button, where it will draw on the screen, how many dps it will skip from top and what text will display on this object.
What about this database schema:
CREATE TABLE Persons ( PersonID int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255) NOT NULL, Address varchar(255), Phone number(20) NOT NULL );
This schema is a very nice example of metadata. It explains about table name, fields type, storage length and so own.
Open your hard disk and right click on any file and select properties or file info. Newly opened window contains metadata (the information about your file: file name, file type, date of creation, date of modification and so on).
How is metadata used?
Every application use metadata in its background. When we create a file and save it, some information (file name, file type, date of creation) stores as a metadata with this file. When you right click on file and select properties, operating system fetches this metadata to display on the screen.
Metadata is used for application preferences also. We interact with word processor (MS Office, Open Office) almost every day. This software contains different small windows in main window (GUI). These small windows help us to make our text nice and well-designed. For example Font window, Paragraph window, Styles and Editing window etc. We hide/show these windows because some features are used very often and some are not relevant to our daily work. We configure this application according to our requirements. This configuration saves as metadata in application’s internal database, So when we reopen this application, it fetches metadata from internal database, decorate GUI and displays everything as we set previously. Typically metadata is used at runtime not at compile time.
What is NOT metadata?
Metadata is not what is written in the text file, but the name, size and author of the file. Metadata is not what you are talking over the phone, but rather the footprint of your call, the number you’ve dialed, your location and duration of the call is metadata. Metadata is not what you have read on website but which website you have visited and which browser was used.