8705 Csci - Spatial Databases (Fall 2001) Group 4 (Manjula Nandiraju, Marcelle Caturia) Project: DRAFT I. Introduction 1.1 Problem Significance TIGER/Line files include geographic and cartographic information extracted from the U.S. Census Department's Topologically Integrated Geographic Encoding and Referencing (TIGER) database. The files have been widely used as a GIS data source in various cartographic -related application fields since their introduction in 1988. Several updated versions have been released since that time, the most recent in the year 2000. The existing TIGER/Line file data structure is quite complicated and difficult to follow. Having a conceptual model to diagram entities, attributes, and relationships would make the data structure more intuitive and easy to understand. The TIGER/Line data structure is based on the relational logical model, so a natural conceptual model should be the Entity-Relationship (ER) model extended with spatial pictograms. 1.2 Project Objective and Problem Statement The overall objective of this project is to develop an ER conceptual data model, extended with spatial pictograms, for the year 2000 version of the TIGER/Line files. Our problem statement is formally defined as follows: Given: Find: Objectives: Constraints: ER model, spatial pictograms. Conceptual model for year 2000 TIGER/Line files. Develop ER conceptual model extended with spatial pictograms. Use entities as defined by year 2000 TIGER/Line file technical documentation, use spatial pic tograms.
1.3 Our Contributions Our contributions to the related literature will be the development of a pictogram-extended ER model, designed specifically for year 2000 version of the TIGER/Line files.
II. Related Work In the course of our literature review, we found no sources specifically describing ER conceptual modeling of TIGER/Line files. However, researched sources did describe the processes of constructing ER conceptual models in general [4,5], and of extending the ER model using spatial pictograms [6,7]. In addition, the logical and physical models of TIGER/Line files were discussed in detail, including file version dating from the year 1990 [2,3] to the year 2000 [1].
III. Alternative Conceptual Models 1.1 ER Model for Existing TIGER/Line 2000 Record Types The existing file structure for TIGER/Line 2000 files is based on the concept of spatial objects (points, lines and polygons) which embody both geometry (coordinate location) and topology (relationships between spatial objects). The TIGER/Line files consist of 17 different record types, representing various attributes of the spatial objects. To demonstrate the record types and their relationships, we created an ER conceptual model for the existing file structure (see Figure 1). Each record type is represented with an ER model "entity" symbol (i.e. rectangle shape). Record types are by "related" certain common key attributes, thus we expressed the relationships between record types by listing common key attributes with the ER model "relationship" symbol (i.e. rhombus shape). Spatial pictograms, based on Shekhar et. al. 1999, were incorporated into the conceptual model to clarify which spatial objects are represented in each record type. 1.2 ER Model Based on TIGER/Line 2000 Feature Class Entities Since the existing TIGER/Line file structure is not actually based on the concepts of "entities" and "relationships" as expressed by the ER model, we propose an alternative way to conceptualize TIGER/Line file features. Our proposed conceptual model is based on the concept of features as entities which are commonly used in the census tabulation process. Such entity categories are described as "Feature Classes" in the TIGER/Line 2000 technical documentation. Our ER conceptual model for feature class entities, extended with spatial pictograms, is provided in Figure 2. Each feature class was divided into various sub-categories. We created an ER conceptual model (see Figure 3) for the "Landmarks" sub-category in order to demonstrate that the individual subcategories can also be modeled. IV. Validation The data structures for the TIGER/Line Files already exist, so we cannot validate our extended ER model by experimentally translating from the conceptual to logical model. However, we will provide an example subset of our ER model with possible resulting data tables. This can be compared with the existing data structure. [Insert resulting data tables]
V. Conclusions and Future Work 5.1 To be developed as project progresses. VI. References ...