Guided Notes Ch. 5 Basic Semantics Ch. 6 Data Types PHP Fundamentals Lecture Notes from both Louden and Sebesta Review questions

Semantics Semantics – what the language construct actually do Specification methods By a language reference manual (most common) By a defining translator (by experiment or simulation, must execute to discover) By a formal definition (ch.13– operational, denotational, axiomatic semantics)

Attributes, Binding, and Semantic Functions Attributes – properties that determine the meaning of a name. Binding – process of associating attribute to a name (binding time: static and dynamic) Semantic Functions –Environment: Names  locations –Symbol table: Name  attributes –Memory: Names  values

Scope rules Scope of a variable – the range of statements in which the variable is visible Static scoping – determined by the program units spatial relationship before execution Dynamic scoping – based on the calling sequence of subprograms only at running time

In-class Exercise for Scoping A exercise from Sebesta Ch. 5 #9 Goal: to understand static and dynamic scoping rules

Aliases, Dangling references, and garbage Aliases – the same object is bound to two different names at the same time Dangling references – a location that has been deallocated but can still be accessed by a program Garbage – memory that has been allocated in the environment but that has become inaccessible to the program

Data Type Definition 1 – A set of values. Definition 2 – a set of values, together with a set of operations on those values having certain properties. Strongly-typed Weakly-typed Untyped or dynamically typed

The Evolution of PHP 1995, PHP 1.0, reflects the concerns at that time: password-protecting pages, easily creating forms, and accessing form data on subsequent pages – no plan to create a scripting language 1996, PHP 2.0, large project demanded better performance and integration, conditional HTML  tag-replacement becomes a parser and end up writing an entire scripting language.

The Evolution of PHP (cont.) 1998 PHP 3.0 since 1997, one man-project becomes team project with many developers 2000 PHP 4.0 Zend engine – abstracting the layer between the language and the web server, adding thread-safety, adding a more advanced two stage parse/execute tag- parsing system More to see PHP site…PHP site

Review questions Define each of following terms and then give an explanation example: Semantics and its specification methods Binding and binding time (static and dynamic) Semantic functions Scoping (static and dynamic) Aliases and garbage Data type Strongly-typed language