Review - Chapter 1 Review - Chapter 1

• What a database is, about different types of • How modern databases evolved from files and file databases, and why they are valuable assets for systems decision making – DBMS’s were developed to address file systems’ – Data are raw facts. Information is the result of inherent weaknesses processing data to reveal its meaning. • Flaws in file system data management • Why database design is important – requires extensive programming – Database design defines the database structure. – system administration complex and difficult – A well-designed database facilitates data management – making changes to existing structures is difficult and generates accurate and valuable information. – security features are likely to be inadequate – A poorly designed database can lead to bad decision – independent files tend to contain redundant data making, and bad decision making can lead to the failure of an organization. • How a database system differs from a file system, and how a DBMS functions within the database system

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Review - Chapter 2 Review - Chapter 2

• Why data models are important • Major data models history, and their advantages – A good DBMS will perform poorly with a poorly and disadvantages designed database – Hierarchical model • A data model is a (relatively) simple abstraction of a • Based on a tree structure composed of a root complex real-world data-gathering environment segment, parent segments, and child segments • Basic data-modeling building blocks • Depicts a set of one-to-many (l:M) relationships – Entities between a parent and its children – Attributes • Does not include ad hoc querying capability – Relationships – Network model attempts to deal with many of the • Business rules and how they affect database design hierarchical model’s limitations

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1 Review - Chapter 2 Review - Chapter 3

– Relational model: • Entities • Current database implementation standard – Entities are basic building blocks of a relational database – Entity set is a grouping of related entities, stored in a table • Much simpler than hierarchical or network design – Relationships between entities are represented by entity – Object model is a basic modeling structure of relationship models object oriented model • Relational Table Characteristics • Classification of Data models by level of – Keys define functional dependencies • Superkey, Candidate key, Primary key, abstraction • Secondary key, Foreign key – Data modeling requirements are a function of • Primary key uniquely identifies attributes different data views (global vs. local) and level of – Functional Dependence data abstraction – Determination – Entity integrity – external, internal, conceptual, logical, physical • Controlled Redundancy – Can link tables by using controlled redundancy

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Review - Chapter 3 Review – SQL Intro (Chapter 7, sections 7.4 & 7.6) • Relational algebra • Basic SELECT Query & special clauses – Relational databases classified according to degree to – Computed columns which they support relational algebra functions • Table relationships – Between, like, null, exist, in – 1:1, 1:M, M:M – Order by • DB MetaObjects • Used to sort output of SELECT statement – Data dictionary • Can sort by one or more columns and use either an – Synonym Tables ascending or descending order – System Catalog – Index Tables • Data retrieval speed can be increased dramatically by using indexes

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2 Review – SQL Intro (Chapter 7, sections 7.4 & 7.6) – Distinct – Group by - works with grouping functions to create reporting subtotals • Numerical Aggregated (Grouping) Functions (Sum, Avg, Min, Max, Count) • Having – similar purpose as a where clause but used on a Group By • SQL Plus Commands – Column, Ttitle, Start, Spool – Remarks – REM, block comments /* …*/ – Set Linesize, Pagesize

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