INFO 340 Lecture 3 Relational Databases

Based on the relational model, grounded in mathematic set theories. Three basic elements: Relation, Tuple, and Attributes (in SQL called Tables, Rows, Columns)

Core Relation Model NameDepartme nt PhoneDOBSex John White Managem ent x12091-Oct-45M Ann Beech Payrollx Nov- 60 F David Ford FinanceX Jul-72M Relation Attributes Tuple

Other Elements in the Relational Model Domain – Specifies the constraints placed upon an attribute or attributes. Degree – The number of attributes in a relation. Cardinality – Number of tuples in a relation. And finally…. Relational database – normalized collection of distinctly named relations.

Relational Keys Main goal is to ensure that each tuple can be uniquely identified. Assume there are 10,000 records in this database. What would be a good way to uniquely identify each row?

Relational Keys How about now? Other ways to uniquely identify -- Composite Key

Relational Keys Superkey - Any attribute set that uniquely identifies Candidate key - –Uniquely identifies –Irreducibility - can’t make it any smaller & still work Primary key - The candidate key that you choose to use Foreign key - An attribute (or set) in a table that matches the candidate key of another table. (Can be the same table).

Relational Keys

Mathematical Definition of Relation Consider two sets, D 1 & D 2, where D 1 = {2, 4} and D 2 = {1, 3, 5}. Cartesian product, D 1 X D 2, is set of all ordered pairs, where first element is member of D 1 and second element is member of D 2. D 1 X D 2 = {(2, 1), (2, 3), (2, 5), (4, 1), (4, 3), (4, 5)} Alternative way is to find all combinations of elements with first from D 1 and second from D 2.

Any subset of Cartesian product is a relation; e.g. R = {(2, 1), (4, 1)} May specify which pairs are in relation using some condition for selection; e.g. –second element is 1: R = {(x, y) | x ∈ D 1, y ∈ D 2, and y = 1} –first element is always twice the second: S = {(x, y) | x ∈ D 1, y ∈ D 2, and x = 2y} Mathematical Definition of Relation

Relational database model means relations between attributes A common misconception is that the “relational” in relational databases refers to the way one table relates to another table via foreign keys. This is not the case! Instead, it refers to the relation between attributes in a relation (table in DB speak).

Integrity Constraints Domain constraints - every attribute has an associated domain Integrity Rules Entity Integrity No attribute of primary key can be null Referential Integrity If a foreign key exists in a relation, it must ‘point’ to something -- ie there must be a candidate value in the home relation

Examples of Attribute Domains

NULL Used to indicate value unknown. This means it doesn’t work in normal comparisons. Null is not Zero or a blank string. Debate rages over whether or not to include NULL. –Opens up a relational model.. No longer closed. Was in E.F. Codd’s original specification

Null example Consider the following: What would the result of asking for rows where HourlyRate != 8.50 return? What about HourlyRate = 8.50 or HourlyRate != 8.50? NameHourlyRate Bob8.50 John12 SueNULL Alice8.50

Donald Rumsfeld, Feb 2002 news briefing “As we know, there are known knowns. There are things we know we know. We also know there are known unknowns. That is to say we know there are some things we do not know. But there are also unknown unknowns, the ones we don’t know we don’t know.”

Examples Cyber-Crime Attribution Database Law enforcement work is being done to identify relationships & patterns of activity with global malware-writers. A database needs to be built that tracks known malware writers, their locations, the nearest educational facility/institute, known aliases, known affiliations, etc. It also must track known malware & its types, ie trojan, worm, rootkit, its size etc. It must track which computers have been attacked, what types they are, what their OS’s are, where they were located at the time of attack, the time of attack itself, the IP addresses and domain names of the boxes. Were the victims firewalled? What type of firewall – built in, external hardware, etc. What was the patch level at the time of attack? Were updates running? How many search engine references are there to this code name? Break this down by specific search engine.

Class Activity Divide into 5 groups (approx people) Give yourself a group name Take 15 minutes to come up with scenario requiring a database. Write it down legibly. –Name 3 canned queries that the database must be able to solve. Write these down as well. At the end of 15 minutes, the first group will give their scenario to the next group. The receiving group will: –On the board, create an ERD with: field names & data types An identified primary key

Homework 1 Due Tue 1/14/08 Page Questions: –3.3, 3.4, 3.5, 3.8 Page 110 – Questions: –4.1, 4.8, 4.9