Data Warehousing

Data Warehouse:

The term Data Warehouse was coined by Bill Inmon in 1990, which he defined in the following way: "A warehouse is a subject-oriented, integrated, time-variant and non-volatile collection of data in support of management's decision making process". He defined the terms in the sentence as follows:

Subject Oriented:

Data that gives information about a particular subject instead of about a company's ongoing operations.

Integrated:

Data that is gathered into the data warehouse from a variety of sources and merged into a coherent whole.

Time-variant:

All data in the data warehouse is identified with a particular time period.

Non-volatile

Data is stable in a data warehouse. More data is added but data is never removed. This enables management to gain a consistent picture of the business.

 

There are three types of data warehouses:

1.Enterprise Data Warehouse - An enterprise data warehouse provides a central database for decision support throughout the enterprise.

2.ODS(Operational Data Store) - This has a broad enterprise wide scope, but unlike the real entertprise data warehouse, data is refreshed in near real time and used for routine business activity. One of the typical applications of the ODS (Operational Data Store) is to hold the recent data before migration to the Data Warehouse.Typically, the ODS are not conceptually equivalent to the Data Warehouse albeit do store the data that have a deeper level of the history than that of the OLTP data.

3.Data Mart - Datamart is a subset of data warehouse and it supports a particular region, business unit or business function.

 

Dot Net -Fundamentals

All applications written with Visual C# are written using the .NET Framework. The .NET Framework provides the class libraries that simplify programming in Visual C#, and it also provides the runtime support you need to execute and manage your code.

 

The .NET Framework

A framework is commonly thought of as a set of class libraries that aid in the development of applications. The .NET Framework is more than just a set of classes. The .NET Framework is targeted by compilers using a wide variety of programming languages.

The .NET Framework is responsible for providing a basic platform that applications can share. This basic platform includes a runtime set of services that oversee the execution of applications. A key responsibility of the runtime is to manage execution so that software written by different programming languages uses classes and other types safely.

The Common Language Runtime

The common language runtime is responsible for managing and executing code written for the .NET Framework. Code that’s compiled with the Visual C# .NET compiler always runs with the help of the runtime and is known as managed code. The runtime is responsible for overseeing all aspects of code execution

Type Safety and the Runtime

The runtime ensures type safety for applications and components. For example, a traditional view of type safety is that a variable that refers to a string shouldn’t occasionally hold an integer value. This sort of type safety is enforced by the Visual C# .NET compiler. Type safety is an important part of the .NET security architecture, and the runtime uses type safety to keep applications working robustly.

Assemblies

Applications built for Windows typically have dependencies on one or more dynamic-link libraries (DLLs). Often these DLLs are components that are shared with other applications, and sometimes these DLLs contain Component Object Model (COM) classes that are registered in the system registry. Unfortunately, when these components are updated or improperly installed, existing applications can be broken—a situation commonly known as “DLL hell”. The .NET Framework seeks to avoid DLL hell through the use of assemblies—self-describing modules that replace the notion of DLLs and executable files (EXEs).

The Visual C# .NET compiler doesn’t generate machine code that can be directly executed on your computer. Instead, your project’s source code is compiled into an assembly.

An assembly has two parts: intermediate language (IL) and metadata.

Intermediate language (IL) contains the executable portion of the program. IL is similar to the output from the first pass of a compiler. Metadata describes the assembly contents. The .NET Framework uses metadata to eliminate the need for component registration. Tools such as Visual C# .NET use metadata to simplify development; tools can simply inspect the assembly’s metadata and determine the types and operations that are exported by the assembly.

Loading External Assemblies

When the common language runtime loads your application, it examines your program’s metadata to determine which external assemblies are required for execution. There are two types of assemblies.

·         Private assemblies  - Used by a single application

·         Shared assemblies - Intended for use by multiple applications.

Using the Global Assembly Cache

Assemblies that are employed by multiple projects can be placed in the global assembly cache, which serves as both a storage location and a registry for shared .NET components. The global assembly cache offers much more flexibility than the registration used by COM, enabling multiple versions and cultures (previously known as locales) of an assembly to be stored.

Conclusion

The .NET Framework includes a large number of classes and other types that are used to develop your application, but the .NET Framework is more than just a class library. It also includes the common language runtime, which manages and supports code written for the .NET platform.

Visual C# is a new object-oriented language in the C family of languages, and it’s easily understood by existing C and C++ programmers. In addition, its clean syntax and simple programming model (much simpler than C++) make it an easy language to learn, even if you’re not currently using C or C++.

UNIX Commands

Home Directory: When you log in you are in your home directory. You can't change your home directory.

Current Directory: Your current, or working directory is the directory you are currently in. To access a file in the current directory, just specify it's name. ( . )

Parent Directory: Is the directory above the directory you are in. Just think of a family tree.( .. )

Absolute pathname: Traces a path from the root to the file. An absolute path always starts with root ( / )

Relative pathname: Traces a path from the working directory (current directory) to a file. A relative pathname never starts with a ( / )

The quickest way to get to your home directory from anywhere in the directory structure is to type (cd)