Lessons 20–21 · 2 lessons · N. I. Taylaqov (general editor), A. B. Akhmedov, M. D. Pardayeva, A. A. Abdug‘aniyev, U. M. Mirsanov. Informatics and Information Technologies, Grade 10, 1st edition. “Extremum-Press”, Tashkent, 2017
20
The concept of a database
Textbook: pp. 44–45
GoalExplains the concepts of a database and a data model; tells the hierarchical, network and relational models and structured data apart.
New words
database: an organised collection of related data stored in a computer · ma’lumotlar omboridata model: the rules for how data are structured and which operations can be done on them · ma’lumotlar modelirelational model: data are kept in tables (rows and columns) linked by key values · relyatsion modelstructured data: data written in an agreed layout, such as columns of a table · tuzilmalashtirilgan ma’lumot
Explanation
A database (DB) is a set of data stored in a computer’s memory, with a definite structure and linked together. It is needed in places such as a library, a school register, an online shop or airport flights, for quick searching, less repetition and many users working at the same time. A data model says how data are structured and which operations can be done on them. In the hierarchical model the data form a tree: each record has one “parent” record (school – classes – students). The network model also has links, but a record may be linked with several records. In the relational model data are kept in tables and the tables are linked by key values; most of today’s databases are based on this model. Data written in an agreed layout (by columns) are structured, while free text is called unstructured: the latter cannot be sorted by name or by year of birth.
Worked examples
A school: the tree “school → classes → students” is a hierarchical model. The link “student ↔ club” is a network model: one student attends several clubs and a club has many students – this is not a tree. In the relational model the tables Students(ID, Name, ClassID) and Classes(ClassID, ClassName) are linked through ClassID.
An unstructured entry: “Bobur Karimov, 2009, Samarkand”. The structured form: Surname = Karimov; Name = Bobur; Year of birth = 2009; City = Samarkand. In the second one “those born in 2009” can be found at once. The names in the examples are invented; do not put real personal data into an open database.
Class activity
“Which model?”: situations are written on cards (an organisation chart, a folder tree, a student ↔ subject table); groups mark each as hierarchical, network or relational and justify the choice.
Practice
1
What is a database?
A set of linked data with a definite structure stored in a computer’s memory.
2
A company hierarchy: director – heads of departments – employees. Which model fits?
hierarchical
3
A table has 5 columns and 30 rows. How many cells does it contain?
150
4
Why are searching and sorting hard with entries written as free text?
The name, year and city are not in separate fields, so the program cannot separate them.