Task 156: .DTD File Format

The .DTD file format is used for Document Type Definitions (DTDs), which define the structure, legal elements, and attributes of XML documents as part of the XML 1.0 specification. DTD files are text-based, typically encoded in UTF-8 or ASCII, and contain a series of markup declarations that form a grammar for validating XML. They can be internal (embedded in XML) or external (separate files), with external subsets optionally starting with a text declaration for version and encoding.

1. Based on the specifications, the properties intrinsic to the .DTD file format are the following structural components and declaration types that define its content and grammar:

• Text Declaration: An optional XML declaration at the start of external DTD files, specifying version (e.g., "1.0") and encoding (e.g., "UTF-8"). Syntax: <?xml version="version" encoding="encoding"?>.
• Element Type Declarations: Define element names and their allowed content models (e.g., EMPTY, ANY, mixed, or children with operators like ?, *, +). Syntax: <!ELEMENT Name contentspec>.
• Attribute-List Declarations: Define attributes for elements, including types (e.g., CDATA, ID, ENUMERATION) and defaults (e.g., #REQUIRED, #IMPLIED, #FIXED). Syntax: <!ATTLIST Name AttDef*>.
• Entity Declarations: Define replaceable content for general or parameter entities, which can be internal (literal value) or external (system/public ID). Syntax: <!ENTITY [ % ] Name EntityDef>.
• Notation Declarations: Define formats for unparsed entities or processing instructions. Syntax: <!NOTATION Name (ExternalID | PublicID)>.
• Processing Instructions: Target-specific instructions for applications. Syntax: <?PITarget data?>.
• Comments: Non-parsable explanatory text. Syntax: <!-- comment -->.
• Conditional Sections: Sections to include or ignore declarations based on parameter entities. Syntax: <![INCLUDE[ declarations ]]> or <![IGNORE[ declarations ]]>.
• Parameter Entity References: References to parameter entities within the DTD for modularization. Syntax: %Name;.

These properties form the core syntax and structure of a .DTD file, with validity and well-formedness constraints ensuring consistency.

1. Two direct download links for example .DTD files:

• https://www.w3.org/TR/html4/loose.dtd
• https://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd

1. Below is an HTML snippet with embedded JavaScript suitable for embedding in a Ghost blog post. It creates a drop zone where a user can drag and drop a .DTD file. The script reads the file as text, uses regular expressions to extract instances of each property from the list above, and dumps them to the screen in a formatted output div. It handles basic extraction (may not perfectly handle deeply nested or malformed content).

1. Below is a Python class for handling .DTD files. It opens the file, reads and decodes the text (assuming UTF-8), extracts the properties using regex, prints them to console, and includes a write method to save modified content (e.g., the original text or user-modified).

import re
import os

class DTDHandler:
    def __init__(self, filepath):
        if not filepath.endswith('.dtd'):
            raise ValueError("File must be a .DTD file")
        self.filepath = filepath
        self.text = None
        self.properties = {}

    def read_and_decode(self):
        with open(self.filepath, 'r', encoding='utf-8') as f:
            self.text = f.read()
        self._extract_properties()
        self.print_properties()

    def _extract_properties(self):
        self.properties = {
            'text_declarations': re.findall(r'<\?xml\s+version="[^"]*"\s*(encoding="[^"]*")?\s*\?>', self.text, re.IGNORECASE),
            'element_declarations': re.findall(r'<!ELEMENT\s+[^>]+>', self.text, re.IGNORECASE),
            'attribute_declarations': re.findall(r'<!ATTLIST\s+[^>]+>', self.text, re.IGNORECASE),
            'entity_declarations': re.findall(r'<!ENTITY\s+[^>]+>', self.text, re.IGNORECASE),
            'notation_declarations': re.findall(r'<!NOTATION\s+[^>]+>', self.text, re.IGNORECASE),
            'processing_instructions': [pi for pi in re.findall(r'<\?[^?]+\?>', self.text, re.IGNORECASE) if not re.match(r'xml', pi, re.IGNORECASE)],
            'comments': re.findall(r'<!--[\s\S]*?-->', self.text, re.IGNORECASE),
            'conditional_sections': re.findall(r'<!\[(INCLUDE|IGNORE)\[[\s\S]*?\]\]>', self.text, re.IGNORECASE),
            'parameter_entity_references': re.findall(r'%[^;]+;', self.text),
        }

    def print_properties(self):
        for key, values in self.properties.items():
            print(f"{key.replace('_', ' ').title()}:")
            for value in values:
                print(value)
            print()

    def write(self, new_filepath=None, modified_text=None):
        filepath = new_filepath or self.filepath
        text = modified_text or self.text
        with open(filepath, 'w', encoding='utf-8') as f:
            f.write(text)
        print(f"Written to {filepath}")

# Example usage:
# handler = DTDHandler('example.dtd')
# handler.read_and_decode()
# handler.write('modified.dtd', '# Modified DTD')

1. Below is a Java class for handling .DTD files. It opens the file, reads and decodes the text (UTF-8), extracts properties using regex, prints to console, and includes a write method for saving.

import java.io.*;
import java.nio.charset.StandardCharsets;
import java.util.*;
import java.util.regex.*;

public class DTDHandler {
    private String filepath;
    private String text;
    private Map<String, List<String>> properties = new HashMap<>();

    public DTDHandler(String filepath) {
        if (!filepath.endsWith(".dtd")) {
            throw new IllegalArgumentException("File must be a .DTD file");
        }
        this.filepath = filepath;
    }

    public void readAndDecode() throws IOException {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(filepath), StandardCharsets.UTF_8))) {
            StringBuilder sb = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                sb.append(line).append("\n");
            }
            text = sb.toString();
        }
        extractProperties();
        printProperties();
    }

    private void extractProperties() {
        properties.put("text_declarations", findMatches("<?xml\\s+version=\"[^\"]*\"\\s*(encoding=\"[^\"]*\")?\\s*\\?>", Pattern.CASE_INSENSITIVE));
        properties.put("element_declarations", findMatches("<!ELEMENT\\s+[^>]+>", Pattern.CASE_INSENSITIVE));
        properties.put("attribute_declarations", findMatches("<!ATTLIST\\s+[^>]+>", Pattern.CASE_INSENSITIVE));
        properties.put("entity_declarations", findMatches("<!ENTITY\\s+[^>]+>", Pattern.CASE_INSENSITIVE));
        properties.put("notation_declarations", findMatches("<!NOTATION\\s+[^>]+>", Pattern.CASE_INSENSITIVE));
        properties.put("processing_instructions", filterPIs(findMatches("<\\?[^?]+\\?>", Pattern.CASE_INSENSITIVE)));
        properties.put("comments", findMatches("<!--[\\s\\S]*?-->", Pattern.CASE_INSENSITIVE));
        properties.put("conditional_sections", findMatches("<!\\[(INCLUDE|IGNORE)\\[[\\s\\S]*?\\]\\]>", Pattern.CASE_INSENSITIVE));
        properties.put("parameter_entity_references", findMatches("%[^;]+;", 0));
    }

    private List<String> findMatches(String regex, int flags) {
        List<String> matches = new ArrayList<>();
        Pattern pattern = Pattern.compile(regex, flags | Pattern.DOTALL);
        Matcher matcher = pattern.matcher(text);
        while (matcher.find()) {
            matches.add(matcher.group());
        }
        return matches;
    }

    private List<String> filterPIs(List<String> pis) {
        List<String> filtered = new ArrayList<>();
        for (String pi : pis) {
            if (!pi.matches("(?i)xml.*")) {
                filtered.add(pi);
            }
        }
        return filtered;
    }

    public void printProperties() {
        for (Map.Entry<String, List<String>> entry : properties.entrySet()) {
            System.out.println(capitalize(entry.getKey().replace("_", " ")) + ":");
            for (String value : entry.getValue()) {
                System.out.println(value);
            }
            System.out.println();
        }
    }

    private String capitalize(String str) {
        return str.substring(0, 1).toUpperCase() + str.substring(1);
    }

    public void write(String newFilepath, String modifiedText) throws IOException {
        String path = (newFilepath != null) ? newFilepath : filepath;
        String content = (modifiedText != null) ? modifiedText : text;
        try (BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(path), StandardCharsets.UTF_8))) {
            writer.write(content);
        }
        System.out.println("Written to " + path);
    }

    // Example usage:
    // public static void main(String[] args) throws IOException {
    //     DTDHandler handler = new DTDHandler("example.dtd");
    //     handler.readAndDecode();
    //     handler.write("modified.dtd", "# Modified DTD");
    // }
}

1. Below is a JavaScript class (ES6) for handling .DTD files. Assuming a Node.js environment (uses fs module), it opens the file, reads/decodes as text, extracts properties, prints to console, and includes a write method.

const fs = require('fs');

class DTDHandler {
  constructor(filepath) {
    if (!filepath.endsWith('.dtd')) {
      throw new Error('File must be a .DTD file');
    }
    this.filepath = filepath;
    this.text = null;
    this.properties = {};
  }

  readAndDecode() {
    this.text = fs.readFileSync(this.filepath, 'utf-8');
    this._extractProperties();
    this.printProperties();
  }

  _extractProperties() {
    this.properties = {
      text_declarations: this.text.match(/<\?xml\s+version="[^"]*"\s*(encoding="[^"]*")?\s*\?>/gi) || [],
      element_declarations: this.text.match(/<!ELEMENT\s+[^>]+>/gi) || [],
      attribute_declarations: this.text.match(/<!ATTLIST\s+[^>]+>/gi) || [],
      entity_declarations: this.text.match(/<!ENTITY\s+[^>]+>/gi) || [],
      notation_declarations: this.text.match(/<!NOTATION\s+[^>]+>/gi) || [],
      processing_instructions: (this.text.match(/<\?[^?]+\?>/gi) || []).filter(pi => !/xml/i.test(pi)),
      comments: this.text.match(/<!--[\s\S]*?-->/gi) || [],
      conditional_sections: this.text.match(/<!\[(INCLUDE|IGNORE)\[[\s\S]*?\]\]>/gi) || [],
      parameter_entity_references: this.text.match(/%[^;]+;/g) || [],
    };
  }

  printProperties() {
    for (const [key, values] of Object.entries(this.properties)) {
      console.log(`${key.replace(/_/g, ' ').replace(/\b\w/g, c => c.toUpperCase())}:`);
      values.forEach(value => console.log(value));
      console.log();
    }
  }

  write(newFilepath = this.filepath, modifiedText = this.text) {
    fs.writeFileSync(newFilepath, modifiedText, 'utf-8');
    console.log(`Written to ${newFilepath}`);
  }
}

// Example usage:
// const handler = new DTDHandler('example.dtd');
// handler.readAndDecode();
// handler.write('modified.dtd', '# Modified DTD');

1. Below is a C++ class (since C does not have native classes, assuming C++ for "c class") for handling .DTD files. It opens the file, reads/decodes as text, extracts properties using std::regex, prints to console, and includes a write method. Compile with C++11 or later.

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <regex>
#include <map>

class DTDHandler {
private:
    std::string filepath;
    std::string text;
    std::map<std::string, std::vector<std::string>> properties;

    std::vector<std::string> find_matches(const std::string& regex_str, int flags = std::regex::icase) {
        std::vector<std::string> matches;
        std::regex rx(regex_str, flags | std::regex::ECMAScript);
        auto begin = std::sregex_iterator(text.begin(), text.end(), rx);
        auto end = std::sregex_iterator();
        for (std::sregex_iterator i = begin; i != end; ++i) {
            matches.push_back(i->str());
        }
        return matches;
    }

public:
    DTDHandler(const std::string& fp) : filepath(fp) {
        if (filepath.substr(filepath.find_last_of(".") + 1) != "dtd") {
            throw std::invalid_argument("File must be a .DTD file");
        }
    }

    void read_and_decode() {
        std::ifstream file(filepath);
        if (!file) {
            throw std::runtime_error("Failed to open file");
        }
        std::string line;
        while (std::getline(file, line)) {
            text += line + "\n";
        }
        file.close();
        extract_properties();
        print_properties();
    }

    void extract_properties() {
        properties["text_declarations"] = find_matches(R"(<\?xml\s+version="[^"]*"\s*(encoding="[^"]*")?\s*\?>)");
        properties["element_declarations"] = find_matches(R"(<!ELEMENT\s+[^>]+>)");
        properties["attribute_declarations"] = find_matches(R"(<!ATTLIST\s+[^>]+>)");
        properties["entity_declarations"] = find_matches(R"(<!ENTITY\s+[^>]+>)");
        properties["notation_declarations"] = find_matches(R"(<!NOTATION\s+[^>]+>)");
        auto pis = find_matches(R"(<\?[^?]+\?>)");
        std::vector<std::string> filtered_pis;
        for (const auto& pi : pis) {
            if (!std::regex_match(pi, std::regex(R"(xml)", std::regex::icase))) {
                filtered_pis.push_back(pi);
            }
        }
        properties["processing_instructions"] = filtered_pis;
        properties["comments"] = find_matches(R"(<!--[\s\S]*?-->)");
        properties["conditional_sections"] = find_matches(R"(<!\[(INCLUDE|IGNORE)\[[\s\S]*?\]\]>)");
        properties["parameter_entity_references"] = find_matches(R"(%[^;]+;)", 0);
    }

    void print_properties() {
        for (const auto& [key, values] : properties) {
            std::string title = key;
            std::replace(title.begin(), title.end(), '_', ' ');
            title[0] = std::toupper(title[0]);
            std::cout << title << ":" << std::endl;
            for (const auto& value : values) {
                std::cout << value << std::endl;
            }
            std::cout << std::endl;
        }
    }

    void write(const std::string& new_filepath = "", const std::string& modified_text = "") {
        std::string path = new_filepath.empty() ? filepath : new_filepath;
        std::string content = modified_text.empty() ? text : modified_text;
        std::ofstream file(path);
        if (!file) {
            throw std::runtime_error("Failed to write file");
        }
        file << content;
        file.close();
        std::cout << "Written to " << path << std::endl;
    }
};

// Example usage:
// int main() {
//     try {
//         DTDHandler handler("example.dtd");
//         handler.read_and_decode();
//         handler.write("modified.dtd", "# Modified DTD");
//     } catch (const std::exception& e) {
//         std::cerr << e.what() << std::endl;
//     }
//     return 0;
// }