Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Oracle Database wikipedia , lookup
Open Database Connectivity wikipedia , lookup
Concurrency control wikipedia , lookup
Microsoft Jet Database Engine wikipedia , lookup
Extensible Storage Engine wikipedia , lookup
Entity–attribute–value model wikipedia , lookup
Clusterpoint wikipedia , lookup
Relational algebra wikipedia , lookup
Rensselaer Polytechnic Institute CSCI-4380 – Database Systems David Goldschmidt, Ph.D. What is a Database? A collection of organized information that persists over a long period of time Such information (or data) is managed by a DataBase Management System DBMS: Software used to create and manage large amounts of data efficiently and securely A typical DBMS is expected to: Provide a means by which users can create databases and specify their schemas Give users the ability to query the database (and efficiently return results) Store huge amounts of data Support durability and reliability, recovering from failures and errors Control user access to data (i.e. security) Database schemas abstract elements of the real world; to do so, we use a data model A data model describes: Structure of the data Operations on the data (reads and writes) Constraints on the data Transactional (and other) databases must meet the ACID test: Atomicity: all-or-nothing execution Consistency: relationships between data elements must adhere to defined constraints Isolation: each transaction appears as if it occurs without other database activity Durability: the data itself is durable in the sense that the data must never be lost A relation is a two-dimensional data structure that consists of a set of attributes and (zero or more) tuples or rows of data attribute1 firstname attribute2 lastname attribute3 office attribute4 nuttiness Mark Goldberg AE 108 6 Mukkai Krishnamoorthy Lally 305 30 Sibel Adali Lally 313 6 Each attribute takes only simple values i.e. strings, numbers, boolean values, dates, etc. The relation schema consists of: The name of the relation The set of attributes The name (and type) of each attribute Other constraints An example: Profs( firstname, lastname, office, nuttiness ) A relation contains a set of tuples Each tuple contains values for all the attributes in the relation schema that are drawn from the domain of that attribute Example tuples: ( 'Mark', 'Goldberg', 'AE 108', 6 ) ( 'Mukkai', 'Krishnamoorthy', 'Lally 305', 30 ) ( 'Sibel', 'Adali', 'Lally 313', 6 ) A key for a relation is a set of attributes such that no pair of tuples has the same value for the key Examples: Social Security Number RIN (Rensselaer ID Number) First and last name (would this one work???) Profs( firstname, lastname, office, nuttiness ) In practice, keys are used to improve efficiency of queries using such keys And note that not all keys provide “uniqueness” Since relations may have multiple keys, a primary key is selected The primary key might be a separate (unused?) numeric field To store a relation, we can use SQL to create a table in a relational database system Example attribute (data) types include: CHAR, VARCHAR, TEXT BIT, INT, INTEGER, FLOAT, DOUBLE, REAL DECIMAL, NUMERIC DATE, DATETIME, TIMESTAMP BLOB, MEDIUMBLOB, LONGBLOB create table tablename ( attribute1_name attribute1_type, attribute2_name attribute2_type, ... attributeN_name attributeN_type, constraints ); create table student ( id int, name varchar(255), major char(4), gender char(1), dob date, constraint student_pk primary key (id) ); Removing a table from the schema: drop table tablename; truncate table tablename; Adding a new attribute to a table: alter table tablename add attributename attributetype; Removing an attribute from a table: alter table tablename drop attributename; Relational algebra consists of a set of simple operators that can be used to query the database Each operator takes as input two relations and produces as output a relation Think of a relation as a set of tuples The input and output relations all must have the same schema Given two relations R and S that have the same schema, set operators include: Union: ▪ R S { tuples that are in R or S (or both) } Intersection: ▪ R S { tuples that are in both R and S } Set difference: ▪ R – S { tuples that are in R but not in S } The projection of a relation R on attributes A1, A2, ..., An is given by: A ,...,A (R) = { t | t is a tuple in R and t only contains values for attributes A1, A2, ..., An iff the schema of R contains attributes A1, A2, ..., An } 1 n We use projection to remove existing attributes from R (by selecting a subset of them) Find and select all tuples from relation R that satisfy some set of conditions Forms the basis of querying a database The selection C (R) is based on Boolean condition C over attributes of relation R Example conditions include: ▪ A = e, A > e, A >= e, A < e, A <= e, A <> e ▪ A1 = A2, A1 <> A2 ▪ Any combination of conditions using AND, OR, NOT Selection selects a subset of tuples in relation R (with the schema unchanged) (R) = { t | t is a tuple in R and t satisfies the condition C on relation R } C Selection conditions can only refer to attributes in the given relation R For conditions spanning multiple relations, we first must combine those relations (i.e. join) Download and install both the Oracle and MySQL database packages noted on the course Web site Design a full schema to store information about celebrities, including: Basic information Relationships (e.g. marriages, flings, etc.) Issues (e.g. drugs, affairs, addictions, etc.)