Security, Privacy and Storage: Appunti di Sistemi

Chapter 5. Storing and organizing information

Database relational database

A database is an organized collection of data and the most used by organizations since database management systems (DBMS) can store different types of “information”. Databases are managed by systems that create, maintain, and use databases. Applications handle the processing of data, so usually, they require data from the DBMS, which provides them, and after the elaboration, data is sent back from the application to the DBMS, which updates the actual databases with the updated information.

Databases can’t be substituted by spreadsheets because the latter cause problems such as data duplication, inconsistent data, difficult data retrieval, and difficult data relations. The main difference between the two is that databases are good at storing and organizing information while spreadsheets are good for analyzing and displaying information visually. Anyway, it is easy to export data from a database into a spreadsheet, so it is possible to use both.

Relational databases

Relational databases store data in the form of connected tables, which are made up of rows (records, a set of fields that all pertain to the same thing) and columns (fields, characteristics of the thing). Each table stores data about a separate thing, and this structure permits flexibility when you have to retrieve data minimizing redundancy (unnecessary repetition of facts). Storing each piece of information only once ensures consistent data. To identify the data, an identifier called a primary key has to be used (with eventual composite primary keys that can also be created ex novo). Because the tables are related to each other, it is important to use foreign keys to combine them.

The fact that in a relational database each row/column intersection can store at most one item of data permits the system to eliminate inconsistency (anomalies or redundant information). The tables can relate to each other with one-to-many, many-to-many (that requires the creation of a new table that links the two related tables), and one-to-one relationships.

A database can be shown visually thanks to an entity-relationship diagram (ERD) that shows the data elements and relationships among them. It is made up of rectangles (tables) with primary keys, foreign keys, and fields written inside. Arrows show the relationships between the tables. Online databases are used by organizations, and not, to reach important information.

Chapter 6. Analyzing information for business decision-making

Decision-making skills become increasingly important because the higher the levels, the more complex they are and they have greater impacts. Making good decisions requires good information; otherwise, the impacts are devastating.