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98% of the teenage population does, will try or has tried smoking pot. If you're one of the 2% who hasn't, copy and paste this into your signature.

bonjour, Bonjour.

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Galagala, Michael G.
ICS 22

1. Data Independence
Logical Data Independence -
Refers to the immunity of external schemas to changes in the conceptual schema
Physical Data Independence -
Refers to the immunity of the conceptual schema to changes in the internal schema

The separation of data from the programs that use the data. Nearly all modern applications are based on the principle of data independence. In fact, the whole concept of a database management system (DBMS) supports the notion of data independence since it represents a system for managing data separately from the programs that use the data. In contrast, it is possible to write applications in which the data being processed is actually represented in the program's source code. This data-dependent approach is very inflexible because it makes it difficult to modify the data and it also makes the data inaccessible to other programs.

2. Internal Schema - describes how the data is stored in the database (space allocation, compression, encryption etc.) and interfaces with the OS to manage files in physical storage
Conceptual Schema- Describes what data is stored and the relationships between data
External Schema - Defines the users view of the data

The three levels correspond to three schemas: there is one internal and one conceptual schema per DB, there can be many external sub-schema

3. A data model is the structure in which a computer program stores persistent information. In a relational database, data models are built from tables. Within a table, information is stored in homogeneous columns, e.g., a column named registration_date would contain information only of type date. A data model is interesting because it shows what kinds of information a computer application can process. For example, if there is no place in the data model for the program to store the IP address from which content was posted, the publisher will never be able to automatically delete all content that came from the IP address of a spammer.
Object-Oriented Model
Object DBMSs add database functionality to object programming languages. They bring much more than persistent storage of programming language objects. Object DBMSs extend the semantics of the C++, Smalltalk and Java object programming languages to provide full-featured database programming capability, while retaining native language compatibility. A major benefit of this approach is the unification of the application and database development into a seamless data model and language environment. As a result, applications require less code, use more natural data modeling, and code bases are easier to maintain. Object developers can write complete database applications with a modest amount of additional effort.

Record-based Logical Models
1. Record-based logical models:
o Also describe data at the conceptual and view levels.
o Unlike object-oriented models, are used to
&#61607; Specify overall logical structure of the database, and
&#61607; Provide a higher-level description of the implementation.
o Named so because the database is structured in fixed-format records of several types.
o Each record type defines a fixed number of fields, or attributes.
o Each field is usually of a fixed length (this simplifies the implementation).
o Record-based models do not include a mechanism for direct representation of code in the database.
o Separate languages associated with the model are used to express database queries and updates.
o The three most widely-accepted models are the relational, network, and hierarchical.
o This course will concentrate on the relational model.
o The network and hierarchical models are covered in appendices in the text.

4. DDL - language enabling the structure and instances of a database to be defined in a human-, and machine-readable form. SQL contains DDL commands that can be used either interactively, or within programming language source code, to define databases and their components

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