Algo>Abstract data type
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Abstract data types (ADTs) define a data type in terms of its possible values and operations, independent of implementation details. An ADT consists of a logical form defining the data items and operations, and a physical form comprising the data structures and algorithms that implement it. Simple data types like integers and characters are ADTs with basic storage structures like memory locations and operations implemented by hardware/software. More complex ADTs require user-defined data structures to organize data in memory or files along with subroutines implementing each operation.
Algo>Abstract data type
- 2. 2 Abstract Data Types Abstract Data Type (ADT): a definition for a data type solely in terms of a set of values and a set of operations on that data type. Each ADT operation is defined by its inputs and outputs. ENCAPSULATION: Hide Implementation details
- 3. 3 Def. e.g. whole numbers (integers) and arithmetic operators for addition, subtraction, multiplication and division. e.g. Flight reservation Basic operations: find empty seat, reserve a seat, cancel a seat assignment Why "abstract?" Data, operations, and relations are studied independent of implementation. What not how is the focus. a collection of related data items together with an associated set of operations Abstract Data Types
- 4. 4 Def. Consists of storage structures (data structures) to store the data items and algorithms for the basic operations. The storage structures/data structures used in implementations are provided in a language (primitive or built-in) or are built from the language constructs (user-defined). In either case, successful software design uses data abstraction: Separating the definition of a data type from its implementation. Abstract Data Types
- 5. 5 Data Structure A data structure is the physical implementation of an ADT. Each operation associated with the ADT is implemented by one or more subroutines in the implementation. Data structure usually refers to an organization of data in main memory. File structure is an organization for data on peripheral storage, such as a disk drive.
- 6. 6 Data Type ADT: Type Operations Data Items: Logical Form Data Items: Physical Form Data Structure: Storage Space Subroutines
- 7. 7 Simple Data Types Memory: 2-state devices ↔ bits 0 and 1 Organized into bytes (8 bits) and words (machine dependent — e.g., 2 bytes). Each byte (or word) has an address making it possible to store and retrieve contents of any given memory location. Therefore: the most basic form of data: sequences of bits simple data types (values are atomic — can't be subdivided) are ADTs. Implementations have: » Storage structures: memory locations » Algorithms: system hardware/software to do basic operations.
- 8. 8 Boolean data Data values: {false, true} In C/C++: false = 0, true = 1 (or nonzero) Operations: and && or || not ! x !x 0 1 1 0 && 0 1 0 0 0 1 0 1 | | 0 1 0 0 1 1 1 1
- 9. 9 Character Data Store numeric codes (ASCII, EBCDIC, Unicode) 1 byte for ASCII and EBCDIC, 2 bytes for Unicode Basic operation: comparison to determine ifEqual, Less than ,Greater than, etc. use their numeric codes (i.e. use ordinal value) ASCII/EBCDIC Unicode
- 10. 10 Integer Data Non-negative (unsigned) integer: Store its base-two representation in a fixed number w of bits (e.g., w = 16 or w = 32) 88 = 00000000010110002 Signed integer: Store in a fixed number w of bits using one of the following representations:
- 11. 11 Sign-magnitude representation Save one bit (usually most significant) for sign (0 = +, 1 = – ) Use base-two representation in the other bits. 88 → _0000000010110000 ↑ sign bit Cumbersome for arithmetic computations –88 → _000000001011000 ↓ 1
- 12. 12 Two's complement representation For negative n (–n): (1) Find w-bit base-2 representation of n (2) Complement each bit. (3) Add 1 Example: –88 1. 88 as a 16-bit base-two number 0000000001011000 Same as sign mag.For nonnegative n: Use ordinary base-two representation with leading (sign) bit 0 2. Complement this bit string 3. Add 1 1111111110100111 1111111110101000 (Flip all bits from rightmost 0 to the end)