CSC 485E/CSC 571 Advanced Databases Introduction

In essence a database is nothing more than a collection of information that exists over a long period of time. Databases are empowered by a body of knowledge and technology embodied in specialized software called a database management system, or DBMS. A DBMS is a powerful tool for creating and managing large amounts of data efficiently and allowing it to persist over long periods of time, safely. Among the most complex types of software available. What’s a database?

1.Allows users to create new databases and specify their schema (logical structure of the data), using a data-definition language. 2.Enables users to query and modify the data, using a query language and data-manipulation language. 3.Supports intelligent storage of very large amounts of data. –Protects data from accident or not proper use. Example: We can require from the DBMS to not allow the insertion of two different employees with the same SIN. –Allows efficient access to the data for queries and modifications. Example: Indexes over a specified fields 4.Controls access to data from many users at once (concurrency), without allowing “bad” interactions that can corrupt the data accidentally. 5.Recovers from software failures and crashes. The database [management] system

They encouraged the user to view the data much as it was stored. The chief models were the Hierarchical and Network. The main characteristic of these models was the possibility of easy jumping or navigating from one object to another through pointers. –E.g. From one employee to his department. However these models didn’t provide a high-level query language for the data. –So, one had still to write programs for querying the data. Also they didn’t allow on-line schema modifications. Early DBMS’s (1960’s)

Codd (1970) A database system should present the user with a view of data organized as tables (also called relations). Behind the scene there could be a complex data structure that allows rapid response to a variety of queries. –But the user would not be concerned with the storage structure. Queries could be expressed in a very high-level language, which greatly increases the efficiency of database programmers. –This high-level query language for relational databases is called: Structured Query Language (SQL) Relational databases

Database Studies Design of databases. –What kinds of information go into the database? –How is the information structured? –How do data items connect? Database programming. –How does one express queries on the database? –How does one use other capabilities of a DBMS, such as transactions or constraints, in an application? –How is database programming combined with conventional programming? Database system implementation. –How does one build a DBMS, including such matters as query processing, transaction processing and organizing storage for efficient access? We’ll focus on this part

Fictitious Megatron 2006 DBMS Stores relations as Unix files Students(name, sid, dept) is stored in the file /home/megatron/students as Smith#123#CS Jones#533#EE Schemas are stored in /home/megatron/schemas e.g. Students#name#STR#id#INT#dept#STR Depts#name#STR#office#str

Megatron sample session mayne$ megatron WELCOME TO MEGATRON 2006 megaSQL% SELECT * FROM Students; Nameiddept Smith123CS Johnson522EE megaSQL%

Megatron sample session II megaSQL% SELECT * FROM Students WHERE id >= 500; Johnson#522#EE megaSQL% quit THANK YOU FOR USING MEGATRON 2006 mayne$

Megatron Implementation To execute SELECT * FROM R WHERE Read file schema to get attributes of R Check that the is semantically valid for R Read file R, –for each line check condition if OK, display If we pipe the result into a file, say T, then add an entry for T in the file /home/megatron/schemas

Megatron Implementation II To execute SELECT office FROM Students, Dept WHERE Students.name = 'Smith' AND Students.dept = Depts.name; Read file schema to get attributes and do semantic check. If Ok, then, for each tuple s in Students for each tuple d in Depts if s and d satisfy the WHERE condition, display the office value from s

What’s wrong with Megatron? Tuple layout on disk: no flexibility for DB modifications. –Change CS to ECON and the entire file has to be rewritten. Search Expensive: no indexes; always read entire relation. Brute­force query processing. –Did we need to look at all pairs of student­dept tuples? No buffer manager: everything comes off of disk all the time. No concurrency control: several users can modify a file at the same time with unpredictable results. No reliability: can lose data in a crash or leave operations half done. Little security: file system protection too coarse.

Architecture of a DBMS The “cylindrical” component contains not only data, but also metadata, i.e. info about the structure of data. If DBMS is relational, metadata includes: –names of relations, –names of attributes of those relations, and –data types for those attributes (e.g., integer or character string). A database also maintains indexes for the data. –Indexes are part of the stored data. –Description of which attributes have indexes is part of the metadata.

What will be covered 1.Secondary Storage Management a)Disks b)Accelerated access c)Handling disk failures d)Arranging data on disk 2.Index Structures 1.B-Trees, Extensible Hash Tables, etc. 2.Multidimensional Indexes (for GIS and OLAP) 3.Query Execution (we concentrate a lot here) a)Algorithms for relational operators b)Join methods. 4.Query Compiler (we concentrate a lot here) a)Algebraic laws for improving query plans. b)Cost based plan selection c)Join orders

What will be covered 5.Concurrency Control a)Pessimistic schemes (locking) b)Optimistic schemes (timestamps) 6.Parallel and Distributed Databases a)Parallel algorithms on relations b)Distributed query processing c)Distributed transactions d)Google’s Map-Reduce framework e)Peer-to-peer distributed search 7.Data Mining a)Frequent-Itemset Mining b)Finding similar items c)Clustering of large-scale data 8.Databases and the Internet a)Search engines b)PageRank c)Data streams d)Data mining of streams