Merge pull request #5 from cmu-db/zilongz

goal & architecture

doc/design_doc.md

@@ -5,10 +5,26 @@
 * Chien-Yu Liu ([email protected])
 
 ## Overview
->What is the goal of this project? What will this component achieve?
-
+### Goal
+The goal of this project is to design and implement a **Catalog Service** for an OLAP database system. The Catalog aims for managing metadata and providing a centralized repository for storing information about the structure and organization of data within the OLAP database. This project aims to produce a functional catalog that adheres to [the Iceberg catalog specification](https://iceberg.apache.org/spec/) exposed through [REST API](https://github.com/apache/iceberg/blob/main/open-api/rest-catalog-open-api.yaml).
 ## Architectural Design
->Explain the input and output of the component, describe interactions and breakdown the smaller components if any. Include diagrams if appropriate.
+We follow the logic model described below. The input of our service come from execution engine and I/O service. And we will provide matadata to planner and scheduler.
+![system architecture](./assets/system-architecture.png)
+### Data Model
+We adhere to the Iceberg data model, arranging tables based on namespaces, with each table uniquely identified by its name. Our goal is to enable multi-versioning, facilitating point-in-time queries and allowing for queries at a specific historical version of the table.
+
+For every table in the catalog, there is an associated metadata file. This file contains a collection of manifests, each of which references the table's information at different points in time. The manifest file is an in-memory, non-persistent component that gets recreated based on on-disk files during service restarts. (If it is not frequently updated, we could dump it to disk every time we update it)
+
+To enhance startup and recovery times, we periodically save the in-memory index to disk. This ensures a quicker restoration process by utilizing the dumped index data.
+![Catalog Data Model](./assets/iceberg-metadata.png)
+
+### Use Cases
+#### Namespace
+create/update/delete namespace. 
+#### Table
+create/update/delete table 
+#### Query Table’s Metadata
+get metadeta by {namespace}/{table}
 
 ## Design Rationale
 * Correctness: