Data Flow Styles

Data Flow Styles

Introduction

•               Availability of data controls the computation

•               The structure is determined by the orderly motion of data from component to component

Variations:

•               Control: push versus pull

•               Degree of concurrency

•               Topology

Example of Data Flow style

SUB –STYLE

1.              Pipes and Filters

2.              Batch Sequential Processing

Dataflow: Pipe-and-Filter

Components (Filters)

•               Read input stream (or streams)

•               Locally transform data

•               Produce output stream (or streams) Connectors (Pipes)

•               Streams, e.g., FIFO buffer

Representation of pipes and filters

Data processed incrementally as it arrives

•               Output can begin before input fully consumed Filters must be independent:

•               Filters do not share state

•               Filters do not know upstream or downstream filters

Pipe-and-Filter: discussion

Strengths:

•               Reuse: any two filters can be connected if they agree on data

•               format

•               Ease of maintenance: filters can be added or replaced

•               Potential for parallelism: filters implemented as separate

•               tasks, consuming and producing data incrementally Weaknesses:

•               Sharing global data expensive or limiting

•               Scheme is highly dependent on order of filters

•               Can be difficult to design incremental filters

•               Not appropriate for interactive applications

•               Error handling difficult: what if an intermediate filter

•               crashes?

•               Data type must be greatest common denominator, e.g. ASCII

Batch Sequential Processing

•               Frequent architecture in scientific computing and business data processing

•               Components are independent programs

•               Connectors are media, typically files

•               Each step runs to completion before next step begins

Representation