.NET metadata

.NET Metadata
From Wikipedia, the free encyclopedia

.NET metadata refers to certain data structures embedded within the Common Intermediate Language code that describes the high-level structure of the code. Metadata describes all classes and class members that are defined in the assembly and all class that will be called for. The metadata for a method contains the complete description of the method, including the class, the return type and all of the method parameters.

A .NET language compiler will generate the metadata and store this in the assembly containing the CIL. When the CLR executes CIL it will check to make sure that the metadata of the called method is the same as the metadata that is stored in the calling method. This ensures that a method can only be called with exactly the right number of parameters and exactly the right parameter types.


Developers can add metadata to their code through attributes, custom and pseudo custom attributes.

A custom attribute is a regular class that inherits from the Attribute class. A custom attribute can be used on any method, property, class or entire assembly with the syntax: [Attribute name(optional parameter, optional name=value pairs)]

A pseudo-custom attribute is used just like regular custom attributes but they do not have a custom handler; rather the compiler has intrinsic awareness of the attributes and handles the code marked with such attributes differently.

Design Consideration for Java Applet

Java Look and Feel Design Guidelines, second edition.

Copyright 2001. Sun Microsystems, Inc. All Rights Reserved.

When establishing applications, we need to consider delivery, accessibility to user, and suits a global audience with minimal effort to localize.

When deciding between an application and an applet, the two main issues you need to consider are distribution and security, including read and write permissions. For applet we must also decide whether to display it in the user's current browser window or in a separate browser window.

Distribution
It is simple for applet, users can access the latest version of the applet from anywhere on the Internet, but the applet must be downland and re-start at the browser each time they needed it. But the browser required to have the JFC or JavaTM Plug-In, or we may need to consider to provide plug-in and non-plug-in configurations for user access.

Security
Applet cannot read or wirte from user's hard disk, they are for displaying web information only, it can be front end for system database.

Placement
For applet we must also decide whether to display it in the user's current browser window or in a separate browser window.

Applet display in the same window
It is suited for users perform a single task and should not include a menu bar which confuses users.

Applet display in the separate window
When the applet involved more than one task. Try to avoid confusion between the browser's menu and controls and the applet's menus and controls. We also need to avoid potential conflicts between mnemonics in the two windows.

LAMP Architecture

BuildingScalable Web Architectures
Aaron Bannert
aaron@apache.org / aaron@codemass.com

LAMP combines Linux, Apache, MySQL, PHP or Perl. It is a layer sturcture just like other web architectures.

The outmost layer to direct connect to Internet is the External Cache layer.
It can be Squid, Apache's Mod_proxy or commercial HTTP accelerator

The web server Tier can be make up of Apache, thttpd, Tux Web Server, IIS, Netscape.
It should have a lot of memory.

Application server Tier provide decoupling code into distrinct services, which may reduce the chance for process bottlenecks.

Database Tier, may use free open source product or commercial product to hand data storage and retrieval.

Internal cache Memcache is suggest becuase it is a distributed cache system and use to store short-lived objects from web or application tier.

It provides load balance for HTTP Caches and Servers, App Servers, and DB Slaves.

LAMP provides Scalability, reliability, low cost, flexible, extandable even for large systems. It allows grow in small steps, stay up when it counts, can grow with needs, have rooms for future expension, low cost used mainly open source applications, high Quality of Service (fast page load), Minimal Downtime, Stability, Redundancy, and Resilience.

Support for AJAX - Microsoft

ASP.NET AJAX Overview

AJAX features is alreay provided in Microsoft ASP.NET.
AJAX scripting compatable with most frequently used browsers
(including Microsoft Internet Explorer, Mozilla Firefox,
and Apple Safari).
ASP.NET 2.0 AJAX already becomes standard features from Microsoft product,
The latest one is ASP.NET 3.5. ,
For new production Like Visual Studio 2008, SharePoint also comes with such capabilities, so that in the near future Microsoft is will going to support AJAX.

Python Database framework - PyDbLite

PyDbLite - a small & fast in-memory database engine - PyDbLite.pyAuthor: Pierre Quentel

While preparing the AJAX project and looking for database solutions, PyDbLite
is one of the possible optional. PyDbLite is a pur-Python in-memory database
engine, use list as query language. It is very simple and easy to implement,
but it will take up memory to hold the database, so it is not suitable for a
large scale database application.

It comes with a Base class and allow us to to create, open, update, delete, query the
database and create index for the database file we need. While creating the database, we do not have to defind data type. PyDbLite will accept any value that can be serialized by the cPickle module.

>> code samples <<
Complete reference

from PyDbLite import Base
db = Base('dummy')
db.create('name','age','size',mode="open" )
db.open()
db.insert(name='homer',age=23,size=1.84)
db.commit()
recs = [ r for r in db if 30 > r['age'] >= 18 and r['size'] < 2 ]

for r in (r for r in db if r['name'] in ('homer','marge') ):
do_something_with(r)

for r in db:
do_something_with(r)

db.create_index('age')
records = db._age[23]
len(db)
db.delete(record)
db.update(record,age=24)
db.add_field('new_field'[,default=v])
db.drop_field('name')
db.fields

Introduction to Ajax framework

http://en.wikipedia.org/wiki/Ajax_framework

AJAX framework helps to develop web applications that using Ajax. The goal of the framework is to provide the Ajax engine to help develop server and client-side functions.

There are a lot of different framework available on the net, they are open source and free. Such as:-


Dojo Toolkit, Modular JavaScript toolkit,


Prototype, a JavaScript framework that provides Ajax and other utilities


Mootools, a compact and modular JavaScript framework best known for its visual effects and transitions


Script.aculo.us, Used with the Prototype Framework, mainly for animations and interface development

Javascript Overview

http://en.wikipedia.org/wiki/JavaScript

Javascript is a script language, used to provide functions that can be embedded or included in HTML documents. It supports most of the syntax from C like if, while, switch etc... It provides dynamic typing, the type of the variable is determined by the value, so we can change the type of the variable by assigning different types of value to it. Objects are associative arrays, such that the representation of an object object.x is equivalent to object["x"], so the values within the object can be add, change or deleted. Javasrcipt use prototypes instead of class when defining object properties, functions and method are the same, but if the function is call with an object, the this keyword is refer to the originated object.

Javascript support variadic functions, which is an indefinite number of parameters can be passed to a function. The function can both access them through formal parameters and the local arguments object. JavaScript also support regular expressions, which provide a concise and powerful syntax for text manipulation that is more sophisticated than the built-in string functions.

In order to execute Javascript, the browser who runs it must comes with a JavaScript engine, an interpreter, to interpret JavaScript source code and executes the script accordingly, since not all the browsers can run the JavaScript, so when we may need to test the compatibility of the browser before running the script.

Javascript mostly run at client's browser, client side application, so it can provide a quick response to user's action and is capable of detecting the user's action like keystrokes input, for which HTML alone is not able to handle it.

The web server, server side application, is another common application of the engine. A JavaScript webserver would expose host objects, typically created by public API, representing a HTTP request and response objects, which a JavaScript program could then manipulate to dynamically generate web pages.

JavaScript and the DOM provide the potential for malicious attack, including cross-site scripting. To counter the risk like that, first, scripts run in a sandbox in which they can only perform Web-related actions, not general-purpose programming tasks like creating files. Second, scripts are constrained by the same origin policy: scripts from one Web site do not have access to information such as usernames, passwords, or cookies sent to another site. Third, stick to the same origin policy.